Spyware is one of the reasons I am exploring the possibility of porting a number of my clients over to Linux. As many of you already know, one of the nastiest versions of this problem is known as CoolWebSearch. Described as one of the most difficult to remove, CoolWebSearch has many spyware removal experts pulling their hair out.

Anti-spyware company Webroot Software said Tuesday that CoolWebSearch self-installs malicious HTML applications and exploits security flaws in IE.

“This has vexed all of us,” said Nick Lewis, managing director of Boulder, Colo.-based Webroot. “For consumers, CoolWebSearch is probably one of the most vicious programs in terms of how nasty it is. It completely hijacks the browser so you can’t do anything.”

CoolWebSearch is the most dangerous program on Webroot’s latest list of the 10 worst spyware and adware threats. Webroot’s list of top 10 threats also includes:

• PurityScan, a program that displays pop-up ads and claims that it can delete pornographic images on the person’s computer.

• Transponder (vx2), an Internet Explorer “browser helper object” that monitors Web browsing and sends relevant advertisements.

• KeenValue, an adware program that collects personal information and sends advertisements to computer users.

• Perfect Keylogger, a monitoring tool that records Web sites visited, keystrokes and mouse clicks. It logs passwords, account numbers and other sensitive information.