How do you remove viruses from your computer?

To remove viruses from a Windows computer, run a full scan with the installed antivirus (Microsoft Defender is built into Windows 10 and Windows 11), then get a second opinion from a free scanner such as ESET Online Scanner, and if the infection persists, run the Microsoft Defender offline scan, which checks the computer before Windows starts. If it’s a company computer, disconnect it from the network first and tell your IT team.

Virus infections remain one of the most widespread computer problems, and their sources have changed little since the first version of this article, in 2011: email, web browsing, programs downloaded from unsafe sources and USB sticks. You can use the steps below not only when you think or know your computer is infected, but also as prevention.

What has changed since 2011?

In 2011, we recommended online scanners launched directly from the browser (ESET Online Scanner in Mozilla Firefox or Internet Explorer, and Bitdefender QuickScan), plus installing Bitdefender Free Edition 2011. Those steps no longer apply:

• Microsoft retired Internet Explorer in June 2022, and in-browser scans no longer exist: free scanners are downloaded and run like ordinary programs;
• the 2011 versions of those antivirus programs no longer receive updates, so they don’t recognize new threats;
• Windows 10 and Windows 11 come with a built-in antivirus, Microsoft Defender, which runs all the time and updates through Windows Update.

The recommendation from back then still stands, though: an antivirus that protects the computer continuously matters more than any occasional scan. Some aggressive viruses lock up a computer so badly that you can no longer run any scanner at all.

How can you tell a computer has a virus?

The most common signs:

• the computer suddenly runs much slower, or the fan kicks in for no reason;
• ad windows pop up, the browser’s home page has changed on its own or extensions you didn’t install have appeared;
• the antivirus is turned off and won’t start again;
• your contacts receive emails or messages from you that you didn’t send;
• files won’t open, have strange extensions, and a message appears demanding money to “unlock” them (ransomware).

How do you remove viruses from your computer, step by step?

1. Disconnect the computer from the network (cable and Wi-Fi) if you suspect a serious infection, especially ransomware, so it doesn’t spread to the other computers and to the company server.
2. Run a full scan with Microsoft Defender. Open the Windows Security app, then go to Virus & threat protection > Scan options > Full scan. The steps are also described on Microsoft’s page about virus and threat protection in the Windows Security app.
3. Get a second opinion. Download a free scanner, for example ESET Online Scanner, which checks and cleans the computer without replacing your existing antivirus. Only download programs like this from the manufacturers’ official websites.
4. Run the offline scan. If the infection persists, choose Microsoft Defender Antivirus (offline scan) under Scan options. The computer restarts and is checked before Windows starts, so even viruses that hide are easier to find. Save any open documents first.
5. Change your passwords from another, clean device: email, bank, work accounts. Some viruses steal the passwords saved in the browser.
6. If the infection doesn’t go away, reinstall Windows, after saving your data. A freshly reinstalled computer is safer than a half-“cleaned” one.

If your files have been encrypted by ransomware, don’t pay the ransom: recover the files from backup. That’s why a 3-2-1 backup policy matters, with a copy outside the office, for example through Backup as a Service.

Do you still need a separate antivirus?

For a home computer, Microsoft Defender, built into Windows, provides good basic protection, as long as Windows keeps receiving updates. If you want a separate free antivirus, Bitdefender Antivirus Free is one option. But don’t install two antivirus programs that both run continuously: they get in each other’s way and slow down the computer.

In a company, we recommend a centrally managed security solution: the IT team sees the alerts from every computer, checks remotely that protection is turned on and steps in before an infection reaches the server.

A word of warning about Windows 10: since October 14, 2025, it no longer receives security updates without the paid ESU (Extended Security Updates) program. Microsoft will keep updating the Defender antivirus signatures on Windows 10 until October 2028, but an antivirus can’t cover the operating system’s own security holes. Compatible computers can upgrade to Windows 11 for free.

When should you call a specialist?

Call a specialist if a company computer holds important data, if the infection comes back after scans or if several computers on the network show the same symptoms. RezolvIT steps in remotely or on site, through our computer repair and helpdesk services. For prevention, you can request a free IT audit, which checks the antivirus, updates and backup on all your company’s computers.

RezolvIT supports the companies it works with, from IT security to employees working remotely.