How to eliminate StrelaStealer malware from the operating system

What is StrelaStealer?

StrelaStealer, as its name implies, is a stealer-type malware. This malicious program specifically targets email account log-in credentials. StrelaStealer was first discovered by DCSO CyTec's researchers in November of 2022. Their findings revealed that this malicious program was distributed using spam mail targeting Spanish-speaking users.

StrelaStealer malware overview

As mentioned in the introduction, StrelaStealer seeks to extract email account log-in credentials. At the time of writing, this program targets Microsoft Outlook and Mozilla Thunderbird email clients.

Following successful infiltration, StrelaStealer searches for "logins.json" (account/password) and "key4.db" (password database) within the "%APPDATA%\Thunderbird\Profiles\" directory - by doing so, it can acquire the credentials for Thunderbird.

Alternatively, if Outlook credentials are targeted - StrelaStealer seeks out the Windows Registry from where it can retrieve the program's key and "IMAP User", "IMAP Server", as well as the "IMAP Password" values. Since the latter is kept in an encrypted form, the malicious program employs the Windows CryptUnprotectData feature to decrypt it prior to exfiltration.

Cyber criminals are particularly interested in email accounts. Not only can these platforms contain highly sensitive data, but they can also serve as a gateway to the content registered through the emails. In other words, via a stolen email - criminals may gain access to connected accounts, platforms, services, and other content.

The unauthorized access can be variously misused for profit. For example, by assuming the identity of a social account's owner (e.g., email, social networking, social media, etc.) - cyber criminals can ask the contacts/friends/followers for loans or donations. Social platforms can also be used to proliferate malware by sharing malicious files/links in posts or via private/direct messages.

Furthermore, finance-related accounts such as those of online banking, money transferring, e-commerce, cryptocurrency wallets, and similar - can be used to make fraudulent transactions or online purchases.

To summarize, StrelaStealer infections can result in severe privacy issues, financial losses, and identity theft.

If you suspect that your device is infected with this or other malware - we strongly recommend using an anti-virus to eliminate it without delay.

Stealer-type malware examples

We have analyzed dozens of stealer-type programs; Medusa, Ducktail, CovalentStealer, Icarus - are just a few of our latest finds. This software can target a broad or an especially narrow range of data. How the information is used - likewise varies based on the type of data obtained and the attackers' aims.

However, regardless of how malware operates - its presence on a system endangers device and user safety. Therefore, it is paramount to remove threats immediately upon detection.

How did StrelaStealer infiltrate my computer?

StrelaStealer has been observed being actively distributed via email spam campaigns. These letters contain infectious attachments carrying the malware in question. Two distinct modes of infection were noted. The attachments are typically ISO format files that have varied contents.

In one instance, it is an executable titled "msinfo32.exe" (note that the name may vary, and this applies to the rest of the filenames provided in this section). The executable side-loads the bundled malware via DLL order hijacking.

The other cases involve ISO files containing HTML and LNK files ("x.html" and "Factura.lnk"). The former is a polyglot file - a multi-format file. The LNK file executes the HTML file twice, firstly as a DLL (which has StrelaStealer embedded) and secondly - as an HTML that displays a fake document on the default browser (screenshot below). This tactic minimizes user suspicion, thus aiding StrelaStealer to evade immediate detection.

However, it is possible that this malware is spread using other methods as well. Generally, malware is proliferated by employing phishing and social engineering tactics. It can arrive in various formats, e.g., executables (.exe, .run, etc.), archives (RAR, ZIP, etc.), Microsoft Office and PDF documents, JavaScript, etc. Once an infectious file is executed, run, or otherwise opened - the infection process is initiated.

The most commonly used distribution techniques include: malicious attachments and links in spam mail, drive-by (stealthy/deceptive) downloads, malvertising, online scams, dubious download channels (e.g., unofficial and freeware sites, P2P sharing networks, etc.), illegal program activation tools ("cracks"), and fake updates.

How to avoid installation of malware?

We highly recommend being cautious with incoming emails, PMs/DMs, and other messages. The attachments and links found in suspect/irrelevant mail must not be opened, as they can be malicious and cause infections.

Furthermore, all downloads must be performed from official and verified channels. We advise activating and updating software using functions/tools provided by legitimate developers, as illegal activation ("cracking") tools and third-party updaters may contain malware.

Another recommendation is to be vigilant when browsing since fraudulent and dangerous online content typically appears ordinary and harmless.

We must stress the importance of having a reputable anti-virus installed and updated. Security programs must be used to run regular system scans and to remove threats and issues. 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 StrelaStealer's ISO file and its contents:

Screenshot of the decoy file displayed by StrelaStealer:

Examples of spam emails spreading StrelaStealer (source: securityintelligence.com):

Update November 20, 2024: Strela Stealer has been updated in the past two years. Although its main goal is the same (to steal email credentials from Microsoft Outlook and Thunderbird), the latest version supports more registry keys to harvest Outlook credentials.

It also has new exfiltration functions: one that collects system info via cmd.exe and the other that uses COM objects to list installed apps from the "AppsFolder". Both the dropped file and app list are encrypted before exfiltration.

Furthermore, threat actors started spreading stolen Ukrainian emails and updated Strela Stealer. They have added the Ukrainian language to keyboard checks and use a new method to scan all layouts. If no match is found, it checks the default locale for "AU" (Australia) or "UA" (Ukraine).

Previously, the malware displayed a subtle error message to avoid raising suspicion. The latest versions now display an "Err 100" message, which appears 5 seconds after execution begins.

Update March 7, 2025 – new phishing campaign distributing StrelaStealer has been discovered. The campaign ran from January to February of 2025. The spam sent out during this operation utilized either legitimate invoice emails forwarded to victims or ones crafted to appear as genuine messages of this kind.

However, instead of including an invoice attachment, the attached ZIP archive was intended to infect recipients' systems with this stealer. It is noteworthy that StrelaStealer campaigns continue to bear a strong geo-targeting aspect.

More information on the infection chain used in this campaign can be found in an article by Dawid Nesterowicz on Trustwave.

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

No, StrelaStealer's removal does not require formatting.

What are the biggest issues that StrelaStealer malware can cause?

The threats posed by a malicious program rely on its abilities and the cyber criminals' goals. StrelaStealer is designed to steal email account log-in credentials. In addition to losing their email accounts, victims can also experience severe privacy issues, financial losses, identity theft, and other serious problems.

What is the purpose of StrelaStealer malware?

Regardless of how they operate, most malicious programs are used to generate revenue. However, this software can also be employed to disrupt processes such as those associated with websites, services, companies, organizations, etc. Aside from profit, malware attacks can be motivated by personal grudges and political/geopolitical reasons.

How did StrelaStealer malware infiltrate my computer?

StrelaStealer has been observed being proliferated in the form of malicious attachments in spam emails. However, other distribution methods are likely. In general, malware is widely spread via drive-by downloads, online scams, malvertising, untrustworthy download sources (e.g., unofficial and freeware sites, Peer-to-Peer sharing networks, etc.), illegal software activation tools ("cracks"), and fake updates. What is more, some malicious programs can self-proliferate through 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 designed to detect and eliminate threats. It is capable of removing practically all known malware infections. However, it must be mentioned that running a complete system scan is essential - since sophisticated malicious software tends to hide deep within systems.