How do I know if my computer has a virus?
When a computer runs very slowly it’s easy to blame it on a virus. This isn’t always the case - sometimes it could just be the wrong settings or a lot of unwanted software ("bloatware") slowing your computer down.
If you're not sure of the cause however it is still best to always play it safe by running through the instructions on this page.
Signs that your computer may have a virus:
- When browsing the web you're constantly redirected to a search engine you don't recognise;
- Web pages (often full of adverts) that you didn't request keep opening in new tabs or windows when you're on the internet;
- Your computer seems to have a life of it's own, with programs starting unexpectedly, internet sessions opening randomly, or emails being sent without your knowledge;
- Your computer’s hard disk is constantly whirring and working overtime;
- Error messages regularly appearing to warn you about missing system or application files;
- Your computer regularly restarts or crashes.
If you think you might have a virus then follow the straightforward steps below. On this page we cover a basic virus scan; if the virus seems more persistant then there's a link at the end to further steps you can take.
Step 1 - Run a virus scan
a) Install a (genuine) antivirus program
If your computer doesn't already have an antivirus program then don't worry, for the purposes of scanning your PC right now you can download one of the many (free!) virus scanners that are available for quick one-off scans. Go ahead and pick any of these:
You can find a list of other reputable antivirus products (along with reviews of their effectiveness - they're not all the same) at www.av-test.org.
Never click on any pop up message claiming your PC is infected & offering virus scans - these are fake and will often actually give you a virus instead.
b) Ensure your antivirus program is up to date
Before running a scan you need to check that your software has the very latest virus definitions (or "signatures").
How to do this varies from program to program but in general, with your antivirus program open, look for options like "Update signatures", "Check for Updates", or "Update virus database".
If you can't find this option anywhere then don't worry; whilst it's a good idea to do this it is just a precaution - all antivirus products should keep themselves up-to-date anyway. And if you've only just downloaded an antivirus product then it should be up to date already.
c) Run the scan
Just like updating your virus signatures, how to run a scan will vary between programs. It should be fairly obvious - look for buttons with labels such as "Run a scan" or "Scan your computer now".
Most antivirus programs offer different levels of scanning; as a first pass just run a quick scan if the option is given. A full in-depth scan can take hours so start with a quick scan (which can take up to half an hour depending on various factors) to see if anything is found.
If you know for sure though that you've just had a nasty virus, such as ransomware, then opt to run the full scan to be certain of being thorough.
Normally you should be able to carry on using your PC at the same time as your computer is being scanned, although it’s probably best to leave it alone to do its thing if you don’t need it.
Step 2 - Check the results
After the scan has finished your antivirus software will display a message on screen with the results. If your antivirus program did find a virus (or viruses) then it will tell you, along with what it did about it. Some possible actions it might have taken include:
- "Cleaned": The virus will have been removed from whichever file had been infected, with the file returned to its original state.
- "Deleted": The virus and any infected file have been permanently deleted.
- "Quarantined": The infected file has been moved to a safe place from where it can’t do any further damage. If necessary the file can be restored at a later date.
- "No action": Occasionally antivirus tools are unable to clean, delete, or quarantine an infection. This may happen for particularly complex viruses, or where your antivirus program doesn’t have the necessary permissions to do what it needs to do.
Check what your antivirus is reporting:
If all viruses were cleaned, deleted, or quarantined:
Happy days! Normally this should be sufficient, although very occasionally your antivirus product may suggest further steps to finish cleaning your system. If this is the case it will give you step-by-step instructions on what to do.
It's always worth reading any guidance from your antivirus program as to what the virus did. This can help determine any follow-on steps you must take, such as changing passwords if it was a password stealing virus or "keylogger".
If a virus was found but couldn’t be treated ("no action"):
In this case you’ll need to manually remove the virus(es) from your computer. This can be tricky but the antivirus software will provide a link to step-by-step instructions for what you need to do.
If no viruses were found:
If no viruses were found then that should be good news! However if you still suspect that your PC has a virus but that it just wasn't found, then head to our page of further checks you can do on your computer.
Step 3 - Recover
If any specific recovery actions are needed to fully remove the virus from your PC then your antivirus software should guide you through those. Regardless of these though, there's a few extra steps that are worth following to fully recover - even after the virus has been cleaned.
Update your computer software
Viruses manage to take hold on your computer by exploiting weaknesses in your software & applications. As manufacturers find or hear about these weaknesses they regularly release updates to fix them - you should always try to keep everything up to date to help prevent future virus infections.
See how to do this with our guide to keeping computer software up to date.
Check your browser settings
If you've noticed strange behaviour when browsing the web, such as being redirected to unusual websites or search engines, then you may want to reset your browser back to its default state.
Some viruses try to change your browser's settings to direct you to pages that are under the virus writers' control - even after you've removed the virus. This might just be to make money from advertising, or it could be an attempt to re-infect your PC.
Click on your favourite web browser below for instructions on how to reset it:
- If you use Windows 8 or 10, press the Windows key (on your keyboard) to open the Start screen and type "inetcpl.cpl", then press Enter.
- If you're on Windows 7, click the Start button (on the bottom left of your screen) and click Run. Type "inetcpl.cpl" and press Enter.
- Next, on the screen that opens, click on the "Advanced" tab. You'll see a button labelled "Reset" (see image) - click this.
- The box that then opens is titled "Are you sure you want to reset all Internet Explorer settings?". Make sure you check the box for "Delete personal settings" - this will reset any changes made by the virus to Edge & Internet Explorer browsers.
- Click Reset to accept this, and when it's finished working click Close.
Click this button
- Launch Chrome & click the 3 dots icon in the top right of the screen, then select "Settings" (it's towards the bottom of the list).
- In the new window, scroll right to the bottom and click "Advanced" (if it's not there then they may already be being displayed).
- Scroll right to the bottom and find the button "Reset settings". Click this, and then click "Reset" in the window that opens.
Click this button
- Launch Firefox & click the 3 horizontal lines icon in the top right of the screen, then click the help icon (the question mark) that's at the bottom of menu that appears.
- Select "Troubleshooting Information" from the list.
- At the top of the page there'll be a button "Refresh Firefox..." (see image). Click this button, and select "Refresh Firefox" again in the warning message that then appears.
- After a few seconds it will complete. Click "Finish" to exit.
Select this to reset Firefox
Consider changing passwords
Some viruses are designed to steal passwords from your computer, either capturing them as you type or by grabbing them from your browser's store.
Because of this it can be a good idea to change your passwords after a virus infection, especially for your most important accounts (such as your bank, social media, and email accounts).
If you know that some of your accounts were directly affected - for example if your friends were receiving spam from your email account - then you should definitely change those ones.
Don't change passwords by visiting websites from your computer if you think it might still be infected; use a friend's computer if yours is taking time to clean. See our guide for changing your passwords safely.
Re-run a virus scan after a few days
Antivirus products are great but they don't always catch everything, especially if the virus is new and hasn't been seen before.
For this reason - whatever the result of the initial virus scan - it's always a good idea to run another scan on your computer after a few days when the antivirus developers are likely to know much more of what to look for. Start with Step 1 again (above) to ensure your antivirus program is up to date.
Viruses can be a pain, and the length of this page may give the illusion that cleaning them takes days, but the reality is that they rarely cause huge trouble. If you have a good antivirus program installed then you can often just let it sit there, silently doing all the work for you.