Brian Livingston writes that ‘ millions of Windows users have unwittingly installed “parasites” when setting up music-sharing programs or other free marketing gimmicks. Some parasite programs harvest fake sales commissions from e-commerce sites. They can also make your PC unreliable and crash-prone.’ InfoWorld

He points us to a British website developer named Andrew Clover at whose site you can test your computer for dozens of different parasite programs

. Here’s a Google parasitology search to take you further. Perhaps the most informative and useful site I found is Nasty Secret.