How to remove Cobalt Strike malware from the operating system?

What is Cobalt Strike?

The Cobalt Strike tool is used to detect system penetration vulnerabilities. The tool itself is supposedly used for software testing to find bugs and flaws, however, cyber criminals often take advantage of such tools, and Cobalt Strike is no exception.

Research shows that these people send hundreds of thousands of spam emails that contain malicious Microsoft Word attachments designed to inject Cobalt Strike into systems.

Cobalt Strike malware overview

Spam campaigns differ and often depend on recipients' locations. For instance, one spam campaign that targets Vietnam delivers an attachment called "Danh Sach Nhan Vien Bien Thu Tien Cong Ty.docx", which roughly translates to "List of Marine Employee Employees.docx".

Another spam campaign, which targets Russian users, delivers an attachment called "Изменения в системе безопасности.doc Visa payWave.doc", which roughly translates to "Security Changes Visa payWave.doc". In any case, the opened attachment encourages users to "Enable Editing" (or to enable macro commands).

Furthermore, once the attachment is opened, it immediately runs a number of PowerShell commands in the system background. These commands essentially connect to a remote server and, after performing a number of actions, ultimately download and install Cobalt Strike into the system.

This tool allows cyber criminals to perform various malicious actions remotely (e.g., upload/download files, record keystrokes, etc.) You can find the full list of features below. In any case, note that the presence of Cobalt Strike can cause various issues. Firstly, cyber criminals might inject viruses into the system (e.g., trojans, ransomware, and so on).

Furthermore, they can steal personal data (including accounts) by recording keystrokes. Criminals might gain access to banks, social networks, emails, and other accounts, thereby stealing victims' identities and money. Users with Cobalt Strike installed on their systems are at significant risk.

If you have recently opened any of the aforementioned (or similar) email attachments, immediately scan the system with a reputable anti-virus/anti-spyware suite and eliminate all detected threats.

Malware in general

There are many viruses distributed using spam campaigns. The list of examples includes (but is not limited to) FormBook, TrickBot, Hancitor, Ursnif, Emotet, Adwind, and AZORult.

These viruses are developed by different cyber criminals and their behavior might differ. Nevertheless, all pose a serious threat to your privacy, computer, and finances. Therefore, eliminate them immediately.

How did Cobalt Strike infiltrate my computer?

As mentioned above, Cobalt Strike is distributed using spam email campaigns. Criminals send emails to hundreds of thousands of users. These emails contain deceptive messages encouraging users to open an attached file (Microsoft Word document) - this results in malware infection.

This is a very common technique for malware distribution, however, the attachment is not always an MS Office document. It might be a JavaScript file, PDF, archive, executable, and so on. Note that none of these infections can occur without users' manual intervention - the user must trigger the infection by opening the attached document.

Therefore, lack of knowledge of these threats and careless behavior are the main reasons for computer infections. Some viruses are distributed using fake software update tools, software cracks, trojans, and unofficial software download sources.

Fake software updaters infect computers by exploiting outdated software bugs/flaws or simply downloading and installing malware rather than updates/fixes. Cracking tools claim to allow users to activate software free of charge, however, they typically infiltrate malware into the system - the 'cracking' feature is a deceptive tactic.

Trojans cause chain infections - they infiltrate computers and continue to inject additional malware. Third party download sources (peer-to-peer [P2P] networks, freeware download websites, free file hosting sites, etc.) are used to present viruses as legitimate software. In this way, criminals trick users into downloading and installing malware.

How to avoid installation of malware?

To prevent this situation, be very cautious when browsing the internet, and downloading, installing, and updating software. Carefully analyze each email attachment received. If the file (or attached link) seems irrelevant or the sender seem suspicious, do not open it. Furthermore, download apps from official sources only, using direct download links.

Third party downloaders/installers often include rogue applications, and thus these tools should never be used. Software cracks should never be used, since cracking software is illegal and can lead to installing malware rather than activating any software. We strongly recommend that you keep installed applications updated.

To achieve this, however, employ implemented features or tools provided by the official developer. We also strongly recommend that you have a legitimate anti-virus/anti-spyware suite installed and running - these tools can detect and eliminate malware before it does any harm.

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.

List of features that Cobalt Strike provides:

• Execute commands
• Lateral Movement
• Log keystrokes
• Mimikatz
• Port scanning
• Privilege escalation
• SOCKS proxy
• Upload/download files

Appearance of a malicious Microsoft Word document (supposedly created by a World Health Organization) used to spread Cobalt Strike malware:

Another malicious MS Word document ("简历.docm") used to spread Cobalt Strike malware:

Example of a spam email used to spread a malicious DocuSign-themed MS Excel document that injects Cobalt Strike malware into the system:

Text presented within:

Subject: Connor from Ensilica Limited

Good morning,

Last we chatted, you asked for that I get back in touch in the end of July.
I may perhaps be 4 weeks earlier, however I determined it'd be well worth checking-in.

I've attached prices together with info sheets which describe the extensive collection of our own goods for your reference. I anticipate hearing from you at the earliest.

Thanks
Connor Bucklin
Ensilica Limited

Screenshot of the attached MS Excel document:

Example of yet another spam email used to spread Cobalt Strike (the attachment is a malicious MS Word document):

Text presented within:

Subject: Past due account invoice message

Hello,

Resulting from our annual report for the previous calendar year, we not too long ago discovered the fact that you still have an delayed sum on your account.

Perhaps you've noticed this specific e-mail previously seeing that it's really the second notification from us, even though we haven't got a payment from you yet still.

Please get your invoice enclosed.

We appreciate your online business,
Lorena Hall

Screenshot of the attached MS Word document:

Update August 20, 2020 - Cyber criminals have recently started distributing Cobalt Strike malware via fake (malicious) VPN software installers that look completely legitimate.

Screenshots of the fake (malicious) VPN software installers used to spread Cobalt Strike malware:

Other malicious MS Excel documents used to spread Cobalt Strike malware:

Update December 16, 2021 - Cobalt Strike has been observed being injected into systems by the Emotet trojan. More information about these developments can be found in our article on the subject.

Update March 16, 2022 - Ukraine's Computer Emergency Response Team issued a warning that Cobalt Strike and other malware have been observed being distributed under the guise of Windows anti-virus updates. Several email spam campaigns were discovered that promoted these fake updates. One variant presents itself as a Ukrainian government agency encouraging recipients to improve their network security by installing "critical security updates". In these emails, the malicious file is titled "BitdefenderWindowsUpdatePackage.exe." and is 60MB in size. There is reason to believe that these developments are part of the cyberwar waged against Ukraine. More information on the new distribution methods used for Cobalt Strike can be found in an article by Bill Toulas on Bleeping Computer.

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 Cobalt Strike malware, should I format my storage device to get rid of it?

No, such drastic measures are unnecessary.

What are the biggest issues that Cobalt Strike malware can cause?

What danger a malware infection poses - depends on the malicious program's capabilities and the cyber criminals' modus operandi. Cobalt Strike can steal sensitive information and cause chain infections. While the former naturally endangers user privacy, the threats posed by the latter can vary. Malicious software of this kind can install trojans, ransomware, cryptominers, and other malware. Furthermore, Cobalt Strike has been notably used to cause ransomware infections, which can result in permanent data loss and financial losses.

What is the purpose of Cobalt Strike malware?

Most malicious programs are used for financial gain. However, other reasons exist, e.g., cyber criminals' amusement, process disruption (websites, services, companies, institutions, etc.), personal reasons (targeting specific individuals/groups), and even political/geopolitical motivations.

How did Cobalt Strike malware infiltrate my computer?

Malware is spread via drive-by (stealthy and deceptive) downloads, online scams, unofficial and freeware download websites, Peer-to-Peer (P2P) sharing networks, spam emails, illegal program activation tools ("cracks"), fake updates, etc. Some malicious software can self-spread 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. However, performing a full system scan is key - since high-end malware can hide deep within systems.