Sometimes computers get viruses. You can be the most vigilant user, but somehow, that one sneaky little piece of code got through, and now your computer is behaving very oddly indeed.
A lot of people assume that picking up a virus automatically writes off your computer, calling for a complete reinstall, and starting again from scratch. But it isn't always that bad. Below are some crucial things to do (and not do) if you think your computer has picked up a virus.
1. Don't panic
It might not be that bad. Prepare to sit down and spend some time working out how to get the virus out.
2. Don't email your friends and tell them all about it
You should definitely not be emailing attachments while your computer is infected, but it's safer to simply not email at all. For one, you don't want to go sharing your virus with your nearest and dearest, and for two, do you really want to be typing in all your log-in details while you have a virus potentially monitoring every key stroke?
3. Don't log in to personal accounts, shop online, or share any personal information
You might not think it matters if your virus can get into your Facebook account or email, but that might offer it an easy way to spread to others. Shopping online or logging into online banking will offer the virus (or its creator) everything it needs to carry out identity fraud.
4. Don't plug in external media
Most viruses seize every chance to replicate themselves. By plugging in an external hard drive, you might just be offering your virus the opportunity it needs to hide elsewhere. Then, once you've cleaned your computer up, in goes the external hard drive and you’re back to square one. Worse, if you need your backups from it after you've been forced to re-install, you run the risk of losing access to most of your files.
Of course, you can't go on like this forever, with no email, no banking, no access to files. But this is only a temporary state of affairs while you get to work cleaning the little so-and-so out.
5. Do isolate yourself on your home or work network
The last thing you want is to allow the virus to spread to other computers or equipment on the network. But don't simply unplug your computer from the wall - you'll probably need internet access to remedy the problem. Switch off file sharing and turn off the network discovery function, which should isolate you but still leave you connected.
6. Do make sure you have all the updates for your OS
You may find that the gap in your security that allowed the virus in has already been patched, so making sure you have all the relevant updates will a) remove your vulnerability and b) potentially restrict the virus’s impact and ability to spread.
7. Do update and run your anti-virus
Once you know your anti-virus is up to date, run a full PC scan to make sure it's clean. If you have had any external media plugged in, keep it plugged in and scan that at the same time, to ensure that the virus has nowhere to hide. To be really vigilant, wait a day or so and re-scan, before you plug anything in.
If all else fails, there is of course the fail-safe - reinstalling your OS. If you need to do that, remember to be careful with your backups. If you keep your files backed up on an external hard drive that's been attached to the infected computer, chances are you will be re-infecting your computer as soon as you try to access them, so it pays to try and keep your external media out of the virus’s way. Just remember - don't panic, and do try to make sure the virus doesn't get a chance to spread. Computer viruses don’t have to destroy everything, so be sensible and follow the advice above to give yourself a fighting chance.
Written by Alex Johnson, a blogger on internet security issues.