A software virus that seduced computer users with an e-mail note proclaiming ''ILOVEYOU'' crippled government and corporate computer networks around the world Thursday and destroyed personal files of music and pictures.
By some estimates, the ''love bug'' infected tens of millions of computers worldwide, spreading not only by e-mail like last year's Melissa virus, but through instant messaging systems that let people chat on the Internet.
New variations of the virus were already circulating by Thursday evening, including one disguised as a joke with an e-mail attachment reading ''Very Funny.''
In another malicious twist, the virus was designed to destroy several types of increasingly popular computer files, including those storing pictures, video and music.
Computer security experts, stunned by the rapid spread of the virus, urged computer users to delete any e-mail with a subject line reading ''ILOVEYOU'' and a message saying ''kindly check the attached LOVELETTER coming from me.''
''I stepped away from my desk for 30 minutes and when I came back, there were 177 people who were in love with me,'' said Ted Canova, news director at WCCO-TV in Minneapolis, who deleted the files and suffered no damage. ''That's in addition to the 200 I had when I signed on today.''
The love bug was activated by opening the ''LOVELETTER'' attachment. It would commandeer a computer's Internet browser to visit a Web page - which was later shut down by its service provider. At the Web site, the bug would download a program that searched for various types of passwords and sent them to an e-mail account that appeared to be based in the Philippines.
''If this is unleashed on your home computer, I hope you have backups. It is a destructive file. Once it has run, it has done its damage,'' said Shawn Hernan, vulnerabilty team manager at the CERT Coordination Center, the government-chartered computer security team at Carnegie Mellon University in Pittsburgh.
The FBI quickly opened a criminal investigation, and agents were trying to verify reports that the outbreak may have begun in Asia, possibly the Philippines.
Computer security firms scurried to post software on their Web sites to scan for the bug and remove it from infected machines.
The virus targets computers running on Microsoft's Windows operating system, attacking the Outlook e-mail program and the Internet Explorer browser, both of which are also made by Microsoft.
It spreads like most e-mail viruses, arriving as a seemingly friendly message, infiltrating a person's computer address book and sending copies of itself to contacts listed.
''It blew through here like a tornado,'' said Lou Fontana, a spokesman for the South Carolina Department of Parks, Recreation and Tourism, where the virus spread to individual terminals. ''There were no survivors.''
But in addition to overwhelming computer networks with the sheer crush of e-mail it generates, the new virus strikes out at some of the most popular new passions on the Internet, destroying digital photographs and music stored with the digital technology known as MP3.
The virus disabled e-mail systems on Capitol Hill and in British parliament. State Department officials found the virus in many of their servers early Thursday and ''shut off our connection with the outside world,'' spokesman Richard Boucher said.
AT&T Corp. shut down an e-mail system serving 145,700 employees.
''We're trying to give our tech support people enough room to find a cleanser and make us pure again,'' said AT&T spokesman Burke Stinson.
In Britain, about 30 percent of company e-mail systems were brought down by the virus, according to Network Associates, a computer security firm. In Sweden, the tally was 80 percent.
''The way we look at the I Love You virus is it's almost like Melissa on steroids,'' said Srivats Sampath, president and chief executive of security firm McAfee.com, a division of Network Associates. ''It's the fastest propagating virus we've seen.''
On the Net: National Infrastructure Protection Center at http://www.nipc.gov/
CERT Coordination Center at http://www.cert.org