Windows wouldn't update on Warren Blake's PC. Nor would system restore work. A malware infection seems likely. Here are some symptoms that could suggest foul play.

I'm received countless letters from readers who think they have a "virus." The problems they describe--Blue Screens of Death, no audio,  grinding sounds inside the PC--can be attributed to virtually anything but malware.

Real malware is generally designed not to be noticed. The people who write these programs don't want you to clean them off of your computer. But if you know what to look for, you can recognize a symptom that might be caused by malware.

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Sometimes it's obvious. Ransomware, such as CoinVault, announces itself clearly. But then, ransomware is basically an extortion racket. It can't make you pay the ransom if it doesn't tell you that it has your data.

But the symptoms for other types of malware are less obvious. Here are some common ones:

Suddenly poor performance. If your PC is running slower than it used to, or it seems to be running an awful lot of stuff in the background, malware could be the cause.

Standard maintenance programs don't work. Malware will often protect itself by disabling programs that might help you identify and remove it. So if programs like Windows Update, Task Manager, your antivirus program, Regedit, System Restore, or Msconfig fail to work, you have reason to be suspicious. I should mention that some of these programs--especially Windows Update--can regularly fail without help from outside bad guys--although if it's one of several programs that fail, malware is likely.

New, unwanted toolbars that won't go away. All sorts of programs might install a new toolbar into your browser, and usually, it's no more than a temporary annoyance. But if you can't turn off the toolbar, or you do turn it off and it soon reappears, there's something more sinister at work.

Your home and search pages change. This is very much like the toolbar problem. If these pages change to something you don't want, and you change them back, but your change doesn't last, something is running that you have to stop.

So what do you do if these signs suggest you have an infection?

First, assume that your antivirus program has been compromised. So scan with something else. Try either the ESET Online Scanner or Trend Micro's HouseCall, neither of which requires installation.

I also suggest you do the scanning in Safe Mode with Networking. That way, the malware is less likely to interfere.