When I came back from holidays there were three icons which had mysteriously appeared on the Windows desktop: Spyware and Malware Protection, Privacy Protector, and Error Cleaner. The computer is now running very slow, with a lot of pop-up messages about internet attacks, adware, malware, and spyware. Can you explain what has happened here? The computer is running Windows XP and Norton Antivirus.

From your description of the issue, it seems that over the holiday period your computer has been infected with some spyware, adware, and other various pieces of malware. Since you only noticed this upon your return, I assume that either you left the computer running while away or someone else has been using the computer. In any case, the end result is the same – massive infection on your computer. This is highlighted by the new icons on your desktop, together with the pop-up messages. Most likely, these pop-up messages are advertisements for anti-spyware and anti-adware software packages which “claim” to clean your computer. Be very wary with these advertisements, as these advertisements are being produced by software which has illegitimately loaded itself on your computer. As such, the software which is advertised to fix your computer is generally bogus and is designed to infect your computer even more, and possibly even cost you money (if they are arrogant enough to charge you for the bogus software).

In any case, we have a few options in this situation. The first is to attempt to clean the malware off the computer. As I mentioned in my reply to Michelle’s question in this column, you should download and install Ad-Aware Free (www.lavasoft.de), Spybot Search & Destroy (www.safer-networking.org), and Windows Defender (www.microsoft.com/downloads). Between these three utilities, you should be able to clean most malware and nasties from your computer. However, you need to be aware that once a computer has been infected with malware you can never trust the machine again, as you will never be certain that the malware has completely been removed from the computer. Therefore, the safest alternative would be to back-up all the data you wish to keep and then completely format the hard drive and reinstall Windows. I appreciate that this is not the most convenient procedure, but it will be the safest in that you can ensure all the remnants of the spyware and malware have been removed.

To ensure that your computer does not get infected again, make sure you are running a firewall as this can generally help to stop such infections.