It should be drilled into you by now: Use antivirus software! These programs—from the best free tools to the paid antivirus software—keep tabs on your Windows PC with scans, real-time monitoring, even heuristic analysis of files and processes so new threats can be identified. It’s imperative, especially with Windows, that you have antivirus installed.

However, even the best antivirus isn’t 100 percent foolproof. A device already compromised by malware could get on your network, people can personally place malware on a system, and some malware lays dormant waiting to attack until just the right time. No one can protect entirely against social engineering or phishing schemes that trick people into clicking on or downloading an infected link or attachment. Hell, there are even rogue scareware programs out there that look like antivirus or antispyware, but when you install them, you get infected! Always download from the source—avoid the third-party download sites.

Sometimes, it’s hard to tell when you’re initially infested with a computer virus. There are plenty of signs you should keep an eye out for—incredibly slow performance where once the PC zipped along, browser pop-ups when no browser is even open, scary warnings from security programs you didn’t install, even ransom demands.

If you suspect, or know with absolute certainty, that you’ve got a malware infection, here are the steps to take, immediately, to remove the malware.

(Note that if you do get a ransom demand, the ransomware involved may have already encrypted your files. The solutions below may eradicate the ransomware, but may not…