Self-Extracting Archive (SFX) Malware

What is a malicious self-extracting archive (SFX) file?

Self-extracting (SFX) archive files have traditionally been used to share compressed data with individuals who do not have the software to unpack and view the contents of a standard archive file. Nevertheless, these files can harbor covert malicious functionality that is not readily apparent to users and may evade detection by technology-based security measures.

Self-Extracting archive (SFX) file

More about malicious self-exxtracting archives

Executable SFX archives operate by adding the content intended for archiving to a decompressor stub, which is executed when the file is run. This stub smoothly unpacks and exhibits the contents of the file, eliminating the need for the user to possess specialized software.

While SFX archives can be utilized by software installers to facilitate installation, malicious entities are increasingly utilizing these archives to bypass security measures and execute malicious code.

Various types of SFX decompressor stubs are currently being employed, contingent on the product utilized to generate an SFX archive, and not all products provide identical functionality. Many of these products are widely accessible and user-friendly.

For instance, 7-Zip and WinRAR are two programs that enable the creation of an SFX archive, each with its own unique version of a decompressor stub and features that can be employed or exploited.

Password-secured SFX archives are typically encountered in commercial settings where a product is employed to encrypt a file and necessitate a password to gain access. The resultant file is frequently an SFX archive with an executable extension that can solely be accessed if the appropriate password is provided.

This same technique for safeguarding files has also been exploited to enable unauthorized access.

A campaign involving the Emotet botnet illustrates how SFX archives have been exploited. In this instance, the botnet distributed an SFX archive that, when opened by a user, would automatically extract a second SFX archive, which was password-protected.

The archive then entered the password, extracted its contents, and executed them without requiring further input from the user. Additionally, a decoy file was displayed to prevent arousing suspicion.

Additional instances of infamous malware that threat actors were seen disseminating through SFX archives include CoinMiner and Quasar RAT.

Threat Summary:
Name	Malicious self-extracting (SFX) archive
Threat Type	Trojan, password-stealing virus, banking malware, spyware, or other malware.
Detection Names (yrqs.sfx.exe file used to deliver malware)	Avast (Win32:Malware-gen), Combo Cleaner (Trojan.GenericKD.49033489), Emsisoft (Trojan.GenericKD.49033489 (B)), Kaspersky (Trojan-Dropper.Win32.Agent.teviwl), Microsoft (Trojan:Win32/Casdet!rfn), Full List (VirusTotal)
Symptoms	The symptoms of a malicious SFX file may vary depending on the specific type of malware that is contained within the file.
Distribution methods	Infected email attachments, malicious online advertisements, social engineering, compromised or untrustworthy pages, etc.
Damage	Stolen passwords and banking information, identity theft, the victim's computer added to a botnet, and more.
Malware Removal (Windows)	To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Combo Cleaner. Download Combo Cleaner To use full-featured product, you have to purchase a license for Combo Cleaner. 7 days free trial available. Combo Cleaner is owned and operated by RCS LT, the parent company of PCRisk.com.

Conclusion

For a considerable period, the self-extracting archive has facilitated the distribution of files to end-users. Nonetheless, it presents a security vulnerability since file contents are not effortlessly verifiable, and it can run commands and executables silently.

Our outlined attack method necessitates only one click and no password input to compromise a target, enabling threat actors to carry out various attacks, including crypto-jacking, data theft, and ransomware.

How did malware in a self-extracting archive (SFX) infiltrate my computer?

Threat actors distribute malicious SFX archives by packaging malware inside an SFX archive and enticing victims to download and open it. They may use various techniques, such as disguising the archive as a legitimate file or hiding it within a phishing email or a fake software update.

In some cases, they may also use password-protected SFX archives that automatically extract and execute their malicious payload without requiring any input from the user. These techniques allow threat actors to distribute malware through SFX archives and compromise their victims' systems.

How to avoid installation of malware?

Ensure that your operating system, applications, and antivirus software are up to date. Be cautious of email attachments (and links in emails). Do not open email attachments from unknown addresses or emails that seem suspicious. Malware can be hidden in attachments such as Word documents, PDFs, or ZIP files.

Avoid clicking on links from unknown sources or links that seem suspicious. Only download software from reputable sources and verify that the website is legitimate before downloading anything. Install reputed antivirus software and keep it up to date to detect and remove malware from your device.

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.

Password-protected SFX generated using WinRAR:

Self-Extracting Archive (SFX) Malware password-protected SFX generated using WinRAR

Password-protected SFX generated using 7zip:

Self-Extracting Archive (SFX) malware password-protected SFX generated using 7zip

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

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.

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.

Run Windows 11 in Safe Mode with Networking

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

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.

Process Explorer showing a suspicious unsigned process running from %AppData%

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.

Autoruns 14.x with Hide Microsoft Entries enabled showing the Logon and Scheduled Tasks tabs

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

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.

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

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.

Combo Cleaner full scan results showing detected threats

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.

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

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.

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

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:

Primary email first - it's the recovery hub for everything else
Banking and financial accounts
Password manager master password (if you use one)
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.

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.

Verifying malware removal in the Windows 11 Task Manager Startup apps tab

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

While formatting your storage device can effectively eliminate malware, it is best to use it as a last option. Before resorting to this drastic measure, it is recommended to try to remove the malware using trustworthy antivirus software.

What are the biggest issues that malware can cause?

Malware can cause many issues, including stealing or corrupting sensitive information. Also, it can slow down or crash systems, significantly disrupting daily operations and productivity. Malware can be used to deliver ransomware, create botnets that can be controlled remotely and used to launch large-scale cyber attacks, and more.

What is the purpose of a malware?

Malware can be used to steal sensitive information such as personal data and financial information, damage or destroy files, disrupt normal system operations, and take control of infected devices. Malware can also be used for fraudulent activities such as phishing attacks or to distribute spam emails. The motivations behind creating and distributing malware can vary.

How did a malware infiltrate my computer?

Malware can infiltrate a computer through various means, such as phishing emails, malicious downloads, and infected websites. Additionally, malware can be spread through removable media such as USB drives or CDs and through network vulnerabilities.

Will Combo Cleaner protect me from malware?

Combo Cleaner can identify and remove nearly all known types of malware, but it should be noted that advanced malware can often hide deep within a system. Therefore, a thorough (full) system scan is required to ensure effective detection and removal.

How to avoid infecting a computer via self-extracting archive file