How to remove Koi Stealer from your computer

What kind of malware is Koi Stealer?

Koi Stealer is an information stealer that is distributed by cybercriminals via email. Once infiltrated, Koi Stealer can capture sensitive information, which is then sent back to the attackers. Cybercriminals can use stolen information for identity theft, financial fraud, and other malicious activities.

More about Koi Stealer

Information stealers like Koi Stealer employ various methods to capture sensitive data from infected computers. One method is keylogging, where the malware records keystrokes made by the user. This allows the attacker to obtain passwords, credit card details, social security numbers, ID card information, and other information typed with the infected computer.

Also, stealers like Koi Stealer can be designed screenshots of information and other elements displayed on the victim's screen, this can include sensitive emails and the details mentioned in the previous paragraph. Also, malware of this type can be created to grab data submitted through web forms (e.g., login forms).

Additionally, stealers can be capable of extracting data from browsers, such as saved passwords, cookies, and autofill information, which can provide attackers with access to various online accounts. Furthermore, information-stealing malware can be used to extract data from messaging, email, and other clients.

Overall, information stealers target a wide range of data. They commonly capture login credentials for online banking, email, social media accounts, gaming, and other accounts. Financial information, such as credit card numbers, bank account details, and cryptocurrency wallets are also a commonly targeted.

Additionally, cybercriminals use stealers to capture personal information like names, addresses, phone numbers, social security numbers, etc. By collecting data, information stealers enable cybercriminals to execute various malicious activities, from unauthorized financial transactions to identity theft.

Conclusion

In conclusion, Koi Stealer poses a significant threat to victims. By targeting sensitive data, this malicious program enables cybercriminals to carry out identity theft, financial fraud, and other activities. Caution and proactive protection strategies are important in mitigating the risks posed by Koi Stealer.

More examples of information stealers are Waltuhium Stealer, Vert Stealer, and Stink Stealer.

How did Koi Stealer infiltrate my computer?

Cybercriminals deliver Koi Stealer through email. At first, they send fraudulent emails regarding a recently placed order. If the recipient replies, threat actors respond with an email containing a link. Opening this link leads to a website asking to solve a CAPTCHA. After solving a CAPTCHA, the page downloads a ZIP file named "wells_fargo_statement.zip" (its name can vary).

The downloaded ZIP file contains a shortcut file. Once opened, this shortcut file downloads the Koi Stealer loader, infecting computers with the information stealer.

How to avoid installation of malware?

Do not respond to suspicious emails (e.g., irrelevant emails from unknown addresses) or open files (or links) in emails of this kind. Download software from official websites and app stores, and avoid using other sources. Never install pirated software or use cracking tools. Avoid interacting with pop-ups, ads, buttons, etc., on shady sites.

Regularly update the operating system and programs. Install reputable security software and keep it up to date. 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.

Initial email used to trick users into downloading Koi Stealer:

Text in this email:

Hey,

I'm writing because I recently placed an order on your site but never received a confirmation email.

I saw the confirmation notice after placing the order, and the payment has been debited from my card, but there's nothing in my spam folder. I'm a bit nervous since I haven't received any further information.

Could you please check if my order went through and deliver the confirmation email?

Thanks for your immediate action. Looking forward to hearing from you at your earliest convenience.

Second email (after the recipient replies to the initial email):

Text in this email:

Subject: Re: Order confirmation email not delivered

Hello,

I hope this message finds you well. I am writing to follow up on my previous email regarding the missing order confirmation letter for my recent purchase. Despite waiting for several days, I have yet to receive any confirmation of my order.

To assist in resolving this issue, I have attached a copy of my bank statement to this email. It shows the payment made to your store on 18th of may.
I kindly request that you verify this payment and provide me with the confirmation letter for my order as soon as possible. If there are any additional details or steps required from my side, please let me know at your earliest convenience.

Thank you for your prompt attention to this matter. I look forward to your swift response.

Best regards,
Ada Gomez

Shared with Google easy-exchange: -

The shortcut file downloaded via the link in the second email containing Koi Stealer:

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

---

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

---

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

---

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

---

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

---

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

Formatting will erase all data on the storage device (including Koi Stealer). It is advisable to run a system scan using a security tool like Combo Cleaner to detect and remove malware.

What are the biggest issues that malware can cause?

Malware can cause privacy breaches, identity theft, monetary loss, ransomware attacks, system disruption, data theft, and other issues.

What is the purpose of Koi Stealer?

The purpose of Koi Stealer is to steal sensitive information from infected computers. This information can include login credentials, browser cookies, financial details, and other personal data.

How did Koi Stealer infiltrate my computer?

Threat actors deliver Koi Stealer via email, starting with a fraudulent message about a fictitious order. If the recipient responds, attackers send another email containing a link. Clicking this link leads to a website that downloads a ZIP file. Inside, a shortcut file designed to download Koi Stealer is placed. If executed, this file infects computers with the stealer.

Will Combo Cleaner protect me from malware?

Yes, Combo Cleaner can detect and remove nearly all known malware infections. However, advanced malware often hides deeply within the system. Therefore, performing a thorough system scan is essential.