Unexpected Crashes: If you’ve ever experienced this, you probably already know the hard way that your system crashing or regularly switching to the terrifying blue screen of death is a major red flag that something is very wrong. If it’s happening to you now, immediately scan your system for infections.
Slow System: If you you’re not running any resource-heavy applications on your system but it’s running slowly anyway, it may be because your system is infected with a virus.
Excessive Hard Drive Activity: Similarly, if you notice a lot of hard drive activity even when your computer is idle, this is a warning sign of a potential infection.
Strange Windows: If strange windows pop up during the booting process, particularly those that warn you of lost access to various drives on your system, something is wrong.
Peculiar Messages: If those troubling dialogue boxes crop up when your system is running alerting you that various programs or files won’t open, this is also a bad sign.
Bad Program Activity: If your programs go missing, are corrupted, or start to open themselves without your initiation, and/or if you receive notification that a program is attempting to access the Internet without your command, this is a serious warning sign that you are the victim of malware.
If you receive notification that a program is attempting to access the Internet without your command, this is a serious warning sign that you are the victim of malware.
Random Network Activity: If your router is constantly blinking indicating a high level of network activity when you aren’t running any significant programs or accessing high amounts of Internet data, something might be wrong.
Erratic Email: If your emails aren’t sent, or you hear from your contacts that they’re getting strange emails from you that you did not send yourself, this is a strong indication that your system has been compromised (or that your email password has been stolen).
Blacklisted IP Address: If you receive notification that your IP address has been blacklisted, consider this about as sure a sign as any that your PC is not in good hands — there’s a very good chance it means your system has been compromised and is being used as one tentacle in far-reaching, spam-sending botnet.
Unexpected Antivirus Disabling: Many malware programs are designed to disable the antivirus suites that would otherwise eradicate them, so if your antivirus system is suddenly not operating this could be a sign of a much larger problem.
