Remove the Quasar remote access tool

What is Quasar?

The Quasar tool allows users to remotely control other computers over a network. Software programs of this type are known as remote access tools (RATs). There both are legitimate and illegal RATs. Quasar is a legitimate tool, however, cyber criminals often use these tools for malicious purposes.

I.e., to steal personal information that could be used to generate revenue. If you suspect that Quasar is installed on the operating system (unintentionally), remove it immediately.

Quasar malware overview

Quasar can be used to access Task Manager, Registry Editor, manage files and startup items, download/upload and execute files, access system information, run various computer commands, log keystrokes, steal passwords and access files stored on the computer. It is a powerful tool that can cause serious problems.

Using Quasar, cyber criminals can access Task Manager and start/end processes, and add programs that run automatically on system startup. Note, the added programs are often malicious. Furthermore, Quasar can be used to download and execute various files.

Cyber criminals can thus infect computers with high-risk malware such as ransomware, trojans or other malicious software. Quasar can operate as a keylogger, since it is capable of recording key presses. This feature is used to steal credentials (logins passwords) of personal, important accounts such as Facebook, email, banking accounts, and so on.

By having access to these accounts, cyber criminals can earn revenue via transactions, purchases, obtaining sensitive information, and so on. In any case, recorded keystrokes can cause serious problems such as financial loss, loss of private information, or access to important accounts.

Furthermore, Quasar is used to shut down or restart the system. This might lead to data loss or other problems. For example, unsaved data in documents or other files might be lost, and so on. This RAT can steal and recover passwords from common browsers such as Google Chrome, Mozilla Firefox, and various FTP clients.

This feature can also steal various important accounts. With access to Registry Editor, cyber criminals who use Quasar can change system and application settings. Note, registry errors can cause a number of problems, including irreversible damage to the operating system.

In summary, Quasar has many functions and, if employed for malicious purposes, can lead to serious issues. Therefore, uninstall this software immediately. Note that this applies only to users who were tricked into installing the program by cyber criminals.

Remote Access Trojan examples

More examples of RATs are Sakula, DarkComet, and FlawedAmmyy. These tools are often used to perform illegal actions (i.e. steal sensitive information and accounts). People with computers infected by RATs often end up experiencing financial, data loss, infections with other malware, and so on. When detected/discovered on the operating system.

How did Quasar infiltrate my computer?

Research shows that cyber criminals proliferate Quasar through spam campaigns and various downloaders (or other dubious download channels). Cyber criminals who use spam campaigns send emails that contain attached files and hope that recipients open them. If opened, the malicious attachments install unwanted, malicious software.

Examples of files that are often used to proliferate malware are Microsoft Office documents, PDF files, executables, JavaScript files, archives such as ZIP, RAR that contain malicious files, and so on. Furthermore, dubious file or software download channels can be used to proliferate malware.

Typically, these are various third party downloaders or installers, unofficial websites, free file hosting websites or freeware download pages, Peer-to-Peer networks (torrent clients, eMule, and so on) and other similar sources. People who open files downloaded from these sources often cause installation of malicious software.

The uploaded files are disguised as harmless and legitimate. Other ways are used to trick people into installing rogue programs including fake update tools, trojans, and unofficial software 'activation' tools. Fake update tools supposedly update software, however, they cause download/installation of other, malicious programs.

They can infect computers by exploiting bugs/flaws of outdated software. Trojans are malicious programs that, once installed, download, install, and proliferate malware. They can only be effective, however, if they are first installed on the system. Unofficial "activators" are used by people who wish to avoid paying for licensed software, however, these tools often proliferate malicious software.

How to avoid installation of malware?

If an email is irrelevant, sent from an unknown, suspicious address, and contains an attachment, handle it carefully. Files attached to these emails of this kind should not be opened. All software should be downloaded from official sources (websites) and no other channels or tools should be trusted.

Update installed software properly: update it with implemented functions or tools created by official software developers. If installed software requires activation, it should not be bypassed using third party activation ('cracking') tools. These are illegal and often used to proliferate and install malicious software.

The operating system can also be protected by regularly scanning it with a reputable anti-virus or anti-spyware suite. If you believe that your computer is already infected, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate infiltrated malware.

Screenshot of Quasar administration panel:

Update August 29, 2019 - Recently, a new spam email campaign distributing the Quasar RAT has been discovered. The campaign presents emails as job application forms and the attachment is usually a Microsoft Word document.

Note, however, that cyber criminals have started using a number of techniques to decrease the chance of being detected by various internet security suites. Firstly, the attachment is password-protected. The email is delivered with a message stating that the attachment is protected with a password, and it also provides this password.

This is done to prevent MS Word from automatically running implemented macros, which can be detected as malicious activity. Furthermore, the macro commands contain hundreds or even thousands of unnecessary ("garbage") base64-encoded code strings.

Cyber criminals inject this random code, since many code analysis tools are likely to crash due to memory overload. Additionally, not all data that is essential to downloading/installing malware is placed in the macro commands. Some information is derived from the metadata of images embedded in the document.

Once the macro runs successfully, user are presented with image(s) displaying an error message, whilst in the background, a malicious self-extracting executable (which contains Quasar RAT's binary file) is downloaded.

Screenshot of the deceptive email:

Text presented within this email:

Hello,

I saw your website and I'm interested in a position.

 

Please see my attached resume.

The password is 123

 

Thank you

Screenshot of the malicious MS Word attachment:

Example of a malicious MS Excel document used to inject Quasar RAT into the system:

Another example of a spam email used to spread Quasar RAT (the attached PDF document contains a link to download an archive (hosted in Dropbox) with a malicious executable inside):

Text presented within:

Subject: Re: NEW ORDER

 

Greetings,

Please find our New Order as discussed with your company.
We are ready to make payment so kindly let us know how soon our order will be ready for shipment.

Anticipating your prompt response.

Thanks and Best regards.

Song Chong Ho
Purchase Manager
SUN-TOOLS LTD

Appearance of Quasar's remote desktop access screen:

Update February 2, 2025 - A new supply chain attack has been discovered with a malicious npm package ("ethereumvulncontracthandler"). Pretending to detect Ethereum smart contract flaws, it deploys Quasar RAT. The package downloads a malicious script from a remote server, which then runs Quasar RAT on Windows systems.

Update May 11, 2026 - Researchers have identified a new Linux variant of Quasar RAT, tracked as QLNX, designed to target software developers. This variant focuses on stealing developer credentials - including authentication tokens for GitHub, AWS, Kubernetes, and Docker, as well as package manager login files and SSH passwords - to gain access to software publishing pipelines.

With stolen credentials, attackers could push malicious code into software packages used by many other people downstream, a technique known as a supply chain attack. The malware also uses rootkit techniques to hide on infected systems and wipes system logs to cover its activity. How victims are initially infected has not yet been determined. (source: thehackernews.com).

How to remove malware manually?

Most trojan infections can be removed by running a full system scan with Combo Cleaner. The full manual procedure below is for cases where automatic removal failed, where you want to verify a scan caught everything, or where the threat has multiple persistence points.

Tools you'll need

Combo Cleaner Antivirus 7-days free trial

Recommended primary scanner. VB100 certified. The 7-day free trial is available.

Microsoft Defender Offline Free · built-in

Built into Windows. Boots to a clean environment to catch rootkits.

Process Explorer Free

From Microsoft Sysinternals. Better than Task Manager - shows full paths and signatures.

Autoruns Free

From Microsoft Sysinternals. Lists every place malware can persist on your system.

Microsoft Safety Scanner (MSERT) Free

Official Microsoft on-demand scanner. Always-current signatures - expires every 10 days.

Phase 1~ 5 min

Contain - limit the damage

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1

Disconnect from the network

30 secNo tool needed

Unplug your Ethernet cable and turn off Wi-Fi. If you're on a laptop, the airplane-mode key works fastest.

Why this matters

Many trojans exfiltrate data - saved browser passwords, banking sessions, screenshots - and accept remote commands. Cutting the network stops both immediately. Keep it disconnected until Phase 4.

2

Boot into Safe Mode with Networking

3 min

Safe Mode loads a minimal set of drivers and stops most malware from auto-running. "With Networking" lets you download tools - re-enable Wi-Fi only after you've booted in.

Windows 11

Open Settings → System → Recovery. Click Restart now next to Advanced startup.

Your computer will restart into the "Choose an option" menu. Click Troubleshoot → Advanced options → Startup Settings → Restart. After the second reboot, press 5 or F5.

Windows 10

Click the Windows logo, hold Shift, click the Power icon and choose Restart. In the Choose an option screen, click Troubleshoot → Advanced options → Startup Settings → Restart. Press F5.

Windows 8

Go to the Start Screen, type Advanced, select Settings → Advanced startup options → Restart now → Troubleshoot → Advanced options → Startup settings → Restart → F5.

Note: Windows 8 reached end-of-life in January 2023 - running on it puts you at much higher risk of reinfection.

Windows 7

Click Start → Shut Down → Restart → OK. As the system boots, press F8 repeatedly until the Windows Advanced Options menu appears, then choose Safe Mode with Networking.

Note: Windows 7 reached end-of-life in January 2020 - running on it puts you at much higher risk of reinfection.

Phase 2~ 15 min

Identify - find what's hiding

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3

Inspect running processes with Process Explorer

Tool: Process Explorer5 min

Download Process Explorer from Microsoft Sysinternals. Run it as Administrator. Click Options → Verify Image Signatures and View → Lower Pane View → DLLs.

Sort by "Verified Signer." Anything unsigned running from %AppData%, %LocalAppData%, %Temp%, or %ProgramData% is suspicious. Right-click → Properties to see the full image path. Right-click → "Search Online" to look up unfamiliar process names.

Why not just Task Manager

Task Manager hides full file paths, doesn't show digital signatures, and groups processes in ways that make malware easy to miss. Process Explorer is the same tool Microsoft engineers use.

4

Map every persistence point with Autoruns

Tool: Autoruns 14.x10 min

Download Autoruns. Right-click Autoruns.exe and choose Run as administrator - without elevation, Autoruns can't inspect protected registry hives.

In the menu, open Options → Hide Microsoft Entries and Options → Hide Empty Locations, then click Refresh.

Modern trojans don't just live in startup. Walk through these tabs and look for unsigned or unfamiliar entries:

• Logon - classic Run/RunOnce keys
• Scheduled Tasks - frequent hiding spot, especially tasks with PowerShell, MSHTA, or rundll32 actions
• Services - unsigned services in non-Microsoft folders
• WMI - Event Subscriptions are a stealthy persistence mechanism (MITRE T1546.003)
• Image Hijacks - Image File Execution Options "Debugger" abuse
• AppInit - DLLs loaded into every GUI process
• Browser plug-ins - unsigned add-ons across all installed browsers

Pro tip

Right-click any suspicious entry → "Jump to Image" to see the actual file. Right-click → "Search Online" opens VirusTotal for the file hash. Don't delete yet - just write down the file paths and entry names. We'll remove them after the scans.

5

Check the hosts file and DNS settings

3 minBuilt into Windows

Trojans often redirect bank, antivirus, and update domains to attacker-controlled servers by editing the hosts file or DNS settings.

Hosts file: Open Notepad as Administrator and open C:\Windows\System32\drivers\etc\hosts. Legitimate entries are commented with #. Any uncommented IP-to-domain mapping is suspicious - especially redirects for microsoft.com, windowsupdate, or your bank.

DNS settings: Open Command Prompt as Administrator and run ipconfig /all. Confirm your DNS servers point to your ISP, your router, or a known public resolver (Cloudflare 1.1.1.1, Google 8.8.8.8). Then open Settings → Network & internet → [your adapter] → DNS server assignment and verify both DNS and DNS over HTTPS (DoH) settings haven't been hijacked.

Why this matters

A clean PC with hijacked DNS is still a compromised PC. You'll think you're at chase.com and you'll be at the attacker's clone.

Phase 3~ 60-90 min

Remove - three scans, one cleanup

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No single antivirus catches everything. The order below is intentional: offline scan first (catches rootkits before Windows fully loads), then on-demand scanners on the running system, then manual cleanup of anything they missed.

6

Run Microsoft Defender Offline

Tool: Built into Windows15 min

Reboot to normal Windows. Open Windows Security → Virus & threat protection → Scan options. Select Microsoft Defender Antivirus (offline scan) and click Scan now. Your computer will restart into a stripped-down environment and scan before the full operating system loads.

Why this comes first

Rootkits and bootkits hide from any scanner running on the same Windows session that's already infected. A pre-boot offline scan sees the disk before the malware can hide itself.

Recommended antivirus

Combo Cleaner

VB100 certified. Includes anti-trojan, registry/persistence scanning, anti-spyware in one pass. The 7-day free trial is available.

Download Combo Cleaner

7

Run Combo Cleaner full system scan

Tool: Combo Cleaner20-40 min

Install Combo Cleaner and run a full system scan (not the quick scan). Let it complete fully, review the detected threats, and apply the recommended actions. Combo Cleaner will quarantine known trojans and registry persistence.

8

Run Microsoft Safety Scanner as a second-opinion scan

Tool: Microsoft Safety Scanner15 min

Download Microsoft Safety Scanner (MSERT.exe), Microsoft's free on-demand tool. The binary expires every 10 days, which means every download has the latest signatures. Run a full scan after Combo Cleaner to catch anything one engine alone might miss.

Why a second scan

Different scanning engines catch different threats. Running an additional Microsoft scan after Combo Cleaner is the single most underused verification step in malware removal.

9

Manually remove anything still listed in Autoruns

Tool: Autoruns10 min

Reopen Autoruns. Anything you flagged in Step 4 that's still present hasn't been caught by the automated scans. For each remaining suspicious entry: right-click → Delete in Autoruns (this removes the persistence registration), then navigate to the file path and delete the actual file. Empty the Recycle Bin.

Important

Some malware files reappear after deletion because something else on the system recreates them. If you delete a file and it returns within minutes, you have a remaining persistence point that Autoruns didn't show - usually a service or scheduled task running under SYSTEM. Re-run the scans from Steps 6-8 or proceed to a clean install (see end of guide).

Phase 4~ 15 min

Recover - restore browsers and security

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10

Reset browsers and clear notification permissions

5 min

Trojans and adware frequently hijack browsers - change the default search engine, install rogue extensions, or grant themselves notification permissions to keep displaying scam pop-ups even after the malware is gone.

• Chrome: visit chrome://settings/reset and click "Restore settings to their original defaults." Then visit chrome://settings/content/notifications and remove any unfamiliar sites.
• Edge: visit edge://settings/reset. Then check edge://settings/content/notifications.
• Firefox: open about:support and click Refresh Firefox (Firefox uses "Refresh," not "Reset"). Then check Settings → Privacy & Security → Permissions → Notifications.

Review installed extensions in each browser and remove anything you don't recognize, especially extensions you didn't install yourself.

11

Re-enable Defender, Tamper Protection, and update everything

10 min

Many trojans disable security software. Open Windows Security → Virus & threat protection → Manage settings and confirm Real-time protection, Cloud-delivered protection, and Tamper Protection are all turned on. Tamper Protection prevents malware from disabling Defender silently.

Then run Windows Update (Settings → Windows Update → Check for updates) and update your browsers and applications. The infection vector that let the trojan in originally usually involves outdated software.

Phase 5~ 15 min + 7 days

Verify & secure

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12

Change passwords from a clean device

20 min⚠ Critical

If the trojan was an info-stealer (Lumma, RedLine, Vidar, and similar are extremely common), assume every password saved in your browser is compromised. Change them from a different, known-clean device - your phone is fine if it's not infected.

Recommended order:

1. Primary email first - it's the recovery hub for everything else
2. Banking and financial accounts
3. Password manager master password (if you use one)
4. Social media, shopping, and remaining accounts

Where available, enable phishing-resistant multi-factor authentication (passkeys / FIDO2 hardware keys / authenticator apps) - SMS-based MFA is bypassable by sophisticated attackers.

13

Verify the clean and monitor for 7 days

5 min + 1 week monitoring

Reconnect to the network and run one final full scan with Combo Cleaner. Open Task Manager (Ctrl + Shift + Esc) and switch to the Startup apps tab - confirm nothing suspicious has reappeared.

Over the next 7 days, watch for symptom recurrence: unexpected high CPU usage, unknown processes returning, browser redirects, or pop-ups. If anything returns, you missed a persistence point and the procedure needs to be repeated - or you may have a deeper compromise that requires a clean install.

When to clean install Windows instead

Manual removal isn't always the right answer. Reinstalling Windows from scratch is the only way to be 100% certain when:

• The malware reappears after every removal attempt
• A bootkit or UEFI rootkit was detected (this class of threat sits below the operating system and survives a normal Windows reinstall)
• A confirmed credential-theft trojan ran with administrator privileges (Lumma, RedLine, Vidar) - the system likely has multiple unknown payloads
• The PC is used for online banking, business email, or anything where partial doubt isn't acceptable

A clean install is a 30-60 minute process: Windows 11 reinstall via Settings → System → Recovery → Reset this PC → Remove everything → Cloud download. Back up documents to external storage first, scan the backup with Combo Cleaner before restoring it, and reinstall applications fresh - never restore them from a backup of the infected system.

Important: Manual removal requires advanced computer skills. If you're not confident identifying system files from malicious files, run an automated scan with Combo Cleaner and Windows Defender and stop there - that path catches the vast majority of consumer trojans without the risk of breaking Windows by deleting the wrong file.

Frequently Asked Questions (FAQ)

My computer is infected with Quasar malware, should I format my storage device to get rid of it?

No, Quasar's removal does not require such drastic measures.

What are the biggest issues that Quasar malware can cause?

Quasar is classified as a RAT (Remote Access Tool/Trojan) - a program designed to enable remote access/control over devices. Hence, it can be variously misused and cause a likewise broad range of problems. Quasar can perform many harmful actions on devices, and it has multiple data-stealing functionalities. Furthermore, this RAT can download/install additional malware. In short, software like Quasar can cause multiple system infections, severe privacy issues, significant financial losses, and identity theft.

What is the purpose of Quasar malware?

Cyber criminals use malware primarily to generate revenue. However, they may also use this software for their own amusement or to disrupt processes (e.g., sites, services, companies, organizations, etc.), accomplish personal grudges, or even launch politically/geopolitically motivated attacks.

How did Quasar malware infiltrate my computer?

The most common malware distribution techniques include: drive-by (stealthy and deceptive) downloads, malicious attachments/links in spam mail, dubious download channels (e.g., freeware and third-party sites, Peer-to-Peer sharing networks, etc.), online scams, illegal software activation tools ("cracks"), and fake updates. Furthermore, some malicious programs are capable of self-spreading via local networks and removable storage devices (e.g., external hard drives, USB flash drives, etc.).

Will Combo Cleaner protect me from malware?

Yes, Combo Cleaner is capable of detecting and eliminating practically all of the known malware infections. It has to be emphasized that performing a complete system scan is essential - since high-end malicious software typically hides deep within systems.