Through its PestPatrol research, CA found that Kazaa posed a greater threat than other programs in its top five spyware list because of its widespread popularity. Kazaa claims that its software has been downloaded 214 million times.
CA gave Kazaa a high "clot factor," its measure of how much a program slows a machine by adding unnecessary registry entries and directories. However, classifying a popular application like Kazaa as spyware is a delicate matter, and CA admits this creates difficulties in attaching labels.
"Kazaa does something useful," said Simon Perry, vice president of security strategy for CA. "I'm not going to say that it doesn't. But turn that around--you're allowing millions of strangers onto your machine. (Kazaa) is No. 1 because of the amount if copies it's got out there."
The company said that any other peer-to-peer file exchange programs, such as Blubster, Gnucleus and WinMX, could also degrade network performance and consume storage space because they are bundled with adware or spyware.
Adware program Ezula came second in the company's top five, beating Adopt.hotbar.com and GameSpy Arcade.
He added that CA used the term "pests" as an umbrella phrase to cover around 30 types of annoying programs.
"Pest is a broader category. It includes spyware, adware and browser help objects. One of the things virus writers don't try is to come and sue you. Some of the producers of spyware we detect say to us 'Why are you claiming my software has any malicious intent?'"
However, CA's Web site clearly lists Kazaa as the top spyware threat. Sharman Networks, Kazaa's distributor, was not immediately available for comment.
Dan Ilett of ZDNet UK reported from London.
