Recently on my home computer advertisements have been appearing for Viagra, software, diet pills, and other various items. How can I stop these from appearing? The computer is running Windows XP.

From the description of this issue it seems that your computer is infected with adware. This is software which usually installs itself without user consent and results in advertisements being displayed on the computer. The reason that I have qualified this, saying that it “usually installs itself without user consent” is because some software informs the user that adware will be installed on the computer with that software. This is normally found in advertisement supported software, where the software is free but with the understanding that advertisements will be displayed within the software (which is a revenue stream for the software developer). This is somewhat of a disputed topic, as some software which is advertisement supported does not explicitly warn the user about this aspect, but is buried deep inside the licence agreement (i.e. that long document that appears when installing software and most users blindingly agree to the terms without reading the entire agreement).

Getting back to your specific question, I imagine that the adware which has installed is most likely not from sponsored software but instead adware that has installed without your consent. This is because sponsored software generally displays advertisements for more reputable products than medications and low-priced software, and also such advertisements normally appear within the sponsored program rather than randomly on the computer screen. Therefore, we should attempt to remove this adware from your computer. To do this we will employ three utilities: Ad-Aware Free (www.lavasoft.de), Spybot Search & Destroy (www.safer-networking.org), and Windows Defender (www.microsoft.com/downloads). These are all free utilities which will scan your computer and hopefully should remove any detected threats. I also suggest that you complete a full virus scan of your computer to ensure that there are no viruses. If you do not have any antivirus software on your computer at the moment then it is essential you get such protection on the computer. If you are looking for a good free solution then AVG Antivirus (free.avg.com) is a good option. However, for even better protection you may wish to consider purchasing a virus scanner such as NOD32 (www.eset.com.au).

Once you have done one round of scanning with the anti-adware and anti-spyware utilities you should reboot the computer and then do another round of scanning, in case any of the pieces of adware have reinstalled themselves on the computer. As a point to note, if you find that your computer exhibits other strange behavior then you should be aware that the level of infection on the computer could be greater than originally envisaged. In particular, you may also have spyware installed on your computer. This is a problem of more concern, as spyware may be tracking what you are doing on your computer and sending personal information back to a third-party. My rule of thumb is that whenever your computer has been infected by adware, spyware, viruses, or any other form of malware, the computer cannot be trusted again. This is because you can never be 100% certain that all the components of the infection or threat have been removed from the computer. As such, when you have a major infection on the computer, regardless of whether you have been able to clean the infection or not, my suggestion is to complete a clean installation of the operating system. To do this you will need to backup any data on the computer that you wish to keep and then format the hard drive and reinstall Windows from scratch. As you can tell, this is a destructive process which will result in all data on your computer being lost. Therefore, it is essential that you backup all important data that you wish to keep before embarking upon this procedure. Even though this may seem like overkill, formatting and doing a clean installation of Windows is the only method to truly ensure that the threat has been removed from the computer.