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10 sure-fire signs your computer has a virus

Lynn Wright / 03 February 2016 ( 25 February 2020 )

Protect your computer from dangerous malware with our checklist of symptoms and signs that show your computer has a virus.

Computer virus
Is your computer running slowly? It could be infected with a virus

Viruses are malicious software – known as malware – that can destroy files, steal personal information and damage your computer. 

Here are the top ten signs your PC has a virus.

1. Unexpected pop-up windows

Unexpected onscreen ads are a typical sign of a virus infection. Not only are they annoying, other malware may lurk inside poised to wreck further havoc. 

Never click on a suspicious pop-up – even if it says ‘a virus was detected’. This is an example of rogueware, which asks you to pay for a program to remove a fake virus but may in fact allow even more malware to be downloaded.

Did you know that your iPhone and iPad could also be targeted by hackers? Read our security tips.

2. Slow start up and slow performance

If your PC is taking longer than normal to start or programs are taking ages to open, then your PC may have a virus. 

If your computer’s performance is sluggish, check first that it isn’t due to a lack of RAM memory or hard disk space. If not, the culprit may be a virus.

Read our tips for speeding up your computer's start-up

3. Suspicious hard drive activity

An excessively active hard disk where it makes continual noise or constantly spins – even though you’re not using your computer nor have any programs running – can be a sign your PC is infected with a virus.

Keep your computer in top condition

4. Lack of storage space

If you suddenly find yourself devoid of storage space on your hard drive, a virus may be doing its utmost to make your computer unusable.

Read our guide to filing documents on your computer

5. Missing files

Some malware cause problems by deleting files and programs or moving them around. Some may encrypt your files so you aren’t able to open them.

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6. Crashes and error messages

If programs start opening and closing automatically, your system freezes or shuts down for no reason, or you see odd error messages, then you may have a virus infection.

Don't lose your files and photos with our guide to protecting valuable data

7. High network activity

If your internet connection is very active even when you’re not using it, a virus may be busy sending information back and forth across the internet.

8. Email is hijacked

If friends start receiving emails or instant messages from your social networks asking them to click on an attachment or link, it’s likely that a virus is attempting to spread to other computers via your accounts. If so, change your passwords immediately.

Read our tips for creating secure online passwords

9. Browser woes

Your web browser becoming sluggish, your home page changing or being redirected to unusual websites are all warning signs of a computer virus infection.

10. Security attacks

Some viruses are designed to disable your computer’s protection. So, if you can’t open or install an anti-virus program or your firewall, your computer may be infected.  

Read our guide to staying safe online

Spot any of these symptoms?

Install and run an anti-virus software program to remove malware. Then set the software to automatically scan your system on a regular basis and keep it up-to-date to protect against the most recent threats. 

Ensure your computer firewall is turned on to block malware attacks via the internet. 

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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.