A lot of today's malware goes to great lengths to avoid notice. But some viruses exhibit symptoms that might as well be a banner advertising the infection. Here are a few of the most common tell-tale symptoms of a virus infection:
1. Your PC slows to a crawl; browsing the Web is extremely slow.
By itself, this symptom can be caused by any number of things (including problems with your ISP that are outside of your control). But when the PC slowdown occurs in conjunction with one or more of the additional symptoms described below, it can be good indication your PC is infected.
2. You are constantly being redirected to websites other than you expected.
Typical symptoms will be redirection to an online pharmaceutical (drug) site, or to sites advertising (fake) antivirus and utility software.
3. Your antivirus software is disabled and you're not able to re-enable it.
Sometimes it's blatantly obvious the antivirus has been disabled; other times you may not be sure. You can easily create an EICAR test file to check whether your antivirus is actually working.
4. You cannot boot into Safe Mode.
Booting in Safe Mode prevents extraneous services and programs - including most malware - from loading at startup. So it's in the best interests of the virus to disable Safe Mode booting as it prevents easy removal of the threat.
5.. Task Manager doesn't work.
Task Manager lets you quickly view and stop running programs and processes. Like Safe Mode, many viruses tend to disable access to Task Manager. When malware has interfered, Task Manager may not appear at all, or it may appear for a second, then quickly disappear.
6. Trouble running certain .exe files.
A lot of malware will hook into the loading sequence, ensuring that the malware itself becomes the handler for any executable. Thus, if you try to download a new antivirus scanner, the malware won't let the setup program run.
7. Can't view folder options menu.
Because malware often uses hidden files and folders, malware often disables viewing of the folder options menu so you can't turn these features on. You can re-enable folder options viewing and change the setting to view hidden files and folders, but that won't resolve the underlying infection. In fact, the virus may just disable the feature as quickly as you're done.
If your PC is exhibiting a combination of the above symptoms, check out these tips for How to Remove a Windows Virus.