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“How do I know if my computer has a virus?”

We all know that computer viruses and malware are bad, but how good are we at recognising the symptoms of an infection?

If you learn the ways that malware can cause your computer to misbehave, you’ll be much better at noticing an infection and stopping it before it can cause too much harm.

It helps to think of computer infections just like human diseases. If you see a runny nose and a raised temperature, it’s obvious that something is wrong, but without further observation you can’t be sure whether you’ve got the flu or just a common cold.

Just like a snotty nostril or a hot forehead, remember these simple tips and you’ll be much better equipped to recognise any infection:

Your computer is running slower

If your computer has suddenly started running dramatically slower, it could be the result of a malware infection. The sluggishness could be caused by a number of factors: your computer could be running the malware in the background (using up your system’s resources), it could be copying itself multiple times to help it spread, or it could simply be designed to slow down your system.

This factor once helped me discover that I was infected with a virus. My computer started slowing down and my large hard drive suddenly became full. The reason? I had downloaded (it’s best not to discuss where from!) a file that contained a virus that kept duplicating itself. Then the new copies started duplicated themselves. Within hours my hard drive was full.

It took two days to delete all the duplicated files.

However, a slow system is not a 100% guarantee you’ve been infected (in fact, apart from being detected by virus checkers, there’s no other 100% accurate method). Computers also tend to slow down with age as programs demand more system resources and users add more and more software on them.

If your internet has suddenly become slower when a certain computer is turned on, but works fine when that system is turned off, it could be a sign that the lethargic PC has been infected with a botnet virus.

Botnet viruses allow remote users to control your computer for nefarious purposes, usually to send fake traffic to shut down websites. Therefore not only could you be infected, but your computer could also be part of a criminal offence.

Your computer has become less reliable

If your computer has become less responsive, or is crashing more than it used to, you could also be infected with malware. This is because malware often attacks your computers’ files to help spread itself, steal your information and avoid detection. The files it changes could be important for your computer to run smoothly, and without them it could run into the problems listed above.

Again, it’s important to remember that other issues can cause your computer to crash or become unresponsive. Incompatible hardware or software (such as computer updates) can cause this response, as can an overheating computer.

No two viruses act the same

The final piece of advice is that no two pieces of computer malware act the same. While some have defining characteristics, others can cause a myriad of symptoms. And some will show no symptoms at all.

I once had a virus that set the “Remote Procedure Call” in Windows to fail. This meant that the computer would restart every 60 seconds – a security feature Microsoft had built in to their Windows XP operating system. It was pretty ironic that a security feature was being used to prevent my computer from being usable for more than one minute at a time.

After some quick clicking, I managed to turn off the Remote Procedure Call restart, remove the virus and curse my bad luck.


In conclusion, it’s vital you get to know your computer and how it works. If it starts acting strangely, and you can’t work out why, it might be the sign of a virus infection. Make sure you run a virus scan.


4 Responses to “How do I know if my computer has a virus?”

  1. Michael says:

    Have you heard of a virus that is labeled VenderAPIRun64.exe? My software won’t detect it and I can not get rid of it!

  2. zzzn says:

    when scanning with malwarebytes how lilkely are you to find any infection that is there? my xp machine is slow, but has been for years, and recently had some system errors and unusual crashes. malwarebytes scanning in normal, not safe mode, finds zilch. could i still be infected, how can i further test?

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