Avoid infecting your system through a fake CAPTCHA verification test

What is the "B, S, Tab, A, F, Enter" CAPTCHA scam?

"B, S, Tab, A, F, Enter" is a CAPTCHA scam. This scheme appears as a pop-up window requesting users to verify that they are not a robot. The genuine CAPTCHA ("Completely Automated Public Turing test to tell Computers and Humans Apart") is a challenge-response test to determine whether the user is human or an automated user (i.e., bot).

These tests are common throughout the Web; hence, CAPTCHA is an often-used disguise for scams. The scheme in question - asks users to press specific keys to bypass the Google Chrome browser warning about a malicious file pending download and to confirm it. This scam has been observed being used to proliferate the Ursnif trojan.

"B, S, Tab, A, F, Enter" scam in detail

The "B, S, Tab, A, F, Enter" scheme aims to trick users into downloading an infectious file. The text presented in this deceptive pop-up requests users to prove that they are not a robot. To continue (with their actions, e.g., to resume watching a video), users are asked to press the following keys - "B", "S", "Tab", "A", "F", and "Enter".

After the sequence is completed, users have to click the "Next" button presented in the scam pop-up. The scheme is designed to distract users from their Chrome browser warning them - that the file they are about to download may harm their computer. This is an automatic browser response when an executable file is about to be downloaded.

The alert has two options, "Keep" and "Discard" - intended to either allow the download or deny it. While the letter keys ("B", "S", "A", "F") do not execute any commands, the "Tab" key highlights the "Keep" option, and "Enter" - confirms this selection. Hence, by following the instructions given by this fake verification process, users inadvertently download malicious files onto their devices.

Scams can be pushed in a wide variety of ways. For example, they can be displayed on deceptive websites, endorsed through intrusive advertisements, spread through spam emails and messages, etc. At the time of research, the "B, S, Tab, A, F, Enter" scam was promoted in a rather intricate manner.

The virulent file was downloaded when users attempted to watch an embedded YouTube video (i.e., said video was not watched on the platform it is hosted on but through a different website). The video in question centered a New Jersey women's prison. When users clicked the play button on the video, the file download was triggered, and the site displayed the "B, S, Tab, A, F, Enter" fake CAPTCHA verification pop-up. The scheme then operated as described previously. If users executed the downloaded infectious file, it jumpstarted Ursnif's infection process.

Ursnif malware functionalities

The Ursnif trojan is designed to steal a broad range of private and sensitive data. This malicious program can extract information from infected systems and certain applications installed onto them.

The targeted data includes (but is not limited to): system information, Internet browsing activity (e.g., URLs visited, pages viewed, search queries typed, etc.), browser cookies, account/platform log-in credentials (i.e., usernames/passwords), and finance-related data (e.g., banking account details, credit card numbers, etc.).

Ursnif can also obtain such information by using its keylogging (i.e., keystroke recording) abilities and by taking screenshots. Furthermore, this malware can clear browser cookies, restart/reboot the system, and perform other actions on the compromised device.

To summarize, by trusting the "B, S, Tab, A, F, Enter" scam, users can experience Ursnif infections - which in turn can result in severe privacy issues, financial losses, and even lead to identity theft. If it is suspected/known that the Ursnif trojan (or other malware) has already infected the system - an anti-virus must be used to remove it immediately.

Online scams in general

The Internet is rife with various scams. Their end-goal is always the same - to generate revenue at victims' expense, yet how that is achieved differs.

Schemes can proliferate malware (e.g., trojans, ransomware, cryptominers, etc.); promote adware, browser hijackers, fake anti-viruses, and other PUAs (Potentially Unwanted Applications); gather personal/vulnerable data (phishing); trick users into making fraudulent transactions (e.g., fake purchases, pay bogus fees, etc.).

This deceptive content also uses a variety of scam models. Fake CAPTCHA verification is common for sites attempting to trick users into enabling their browser notifications (e.g., captchaverifier[.]top, boffero[.]com, uniqdatacaptcha[.]top, newssysstem[.]org, etc.).

Other popular models are: warnings that the device is infected (e.g., "Code 0x03A10 (0E10)", "Access to this pc has been blocked for security reasons", etc.), alerts that a software product is outdated/missing (e.g., "Fake flash player update", "Important Defender update available", etc.), hoax prize giveaways and reward programs (e.g., "SPIN FOR REWARD", "Mr Beast Giveaway", etc.), and so on.

How did malware infect my computer?

"B, S, Tab, A, F, Enter" scam infects devices through the use of social engineering. However, malware is proliferated using a wide variety of techniques and tactics. In addition to deceptive/scam webpages, malicious programs are also spread via other dubious download sources such as Peer-to-Peer sharing networks, unofficial and freeware sites, etc.

Malicious software can be disguised as or bundled with ordinary content. Illegal activation tools ("cracks") and fake updates are prime examples. "Cracking" tools can infect systems instead of activating licensed products. Fake updaters cause infections by abusing outdated software flaws and/or by installing malware rather than the updates.

Spam campaigns are used to distribute malware as well. This term defines a mass-scale operation during which thousands of scam emails are sent. The letters can have virulent files attached to them, or the emails contain download links of malicious content.

Infectious files can be in various formats, e.g., executables (.exe, .run, etc.), archives (ZIP, RAR, etc.), Microsoft Office and PDF documents, JavaScript, and so on. When the files are executed, run, or otherwise opened - the infection process is initiated.

How to avoid installation of malware?

It is strongly advised to exercise caution when browsing and download only from official/verified sources. Additionally, all programs must be activated and updated with tools provided by genuine developers. Suspect and irrelevant emails must not be opened, especially any attachments or links found in them.

It is crucial to have a dependable anti-virus/anti-spyware suite installed and kept up-to-date. This software has to be used to perform regular system scans and to remove threats. If you've already opened the file downloaded through the "B, S, Tab, A, F, Enter" CAPTCHA scam, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate infiltrated malware.

Screenshot of the fake "B, S, Tab, A, F, Enter" CAPTCHA displayed on a video:

Screenshot of VirusTotal detections of the malicious file distributed via the "B, S, Tab, A, F, Enter" CAPTCHA scam:

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.