Elinor Abreu

Virus writers have learned what motivates people on-line: sex. A recent virus attached to an e-mail purported to show a movie of someone's naked wife, sending itself to the victims' friends and deleting important Windows system files so that victims have to reinstall the operating system.

The person believed to be responsible for the "Tennis" virus that on Monday spread through thousands of computers said he meant no harm and that he created it to teach computer users a lesson about safe online practices.

Confirming suspicions that the attacks on CNN.com, Yahoo.com Inc. and a handful of other popular Web sites...