In Britain, about 30 percent of company e-mail systems were brought down by the virus, according to Network Associates, another computer security firm. In Sweden, the tally was 80 percent.

Experts said they were stunned by the speed and wide reach of the virus -- and nobody seemed to know of an immediate cure.

"It may be the most comprehensive spreading that I have seen," said Snorre Fagerland of the computer security company Norman in Oslo, Norway, where the virus struck an untold number of companies.

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."

Apple Macintosh computers were declared immune, as were other e-mail programs such as Netscape.

Outlook users who receive an e-mail with "ILOVEYOU" in the subject line are advised not to open the attachment, "LOVE-LETTER-FOR-YOU.TXT."

If they do, the virus replicates itself, apparently sending copies of itself to everyone in the user's e-mail address book. The resultant flood of meaningless e-mails slows down systems and makes it difficult to use e-mail for actual communication.

Because it only infects a PC when the attachment file is opened, the ILOVEYOU virus is less communicable than the November 1999 "Bubbleboy" virus: Exploiting Outlook's message-preview function, Bubbleboy could infect users' PCs even if they did not open the message. The "Love" virus is activated only when the user double-clicks on the attachment.

But ILOVEYOU has a devilish side that Bubbleboy didn't: If a user opens the "Love Letter," the virus attacks multimedia files that were previously stored on the PC -- such as JPEG and GIF image files and MP3 sound files -- and replaces them with dummy versions that contain the virus.

"It is less easily transmitted than other viruses, but if your computer is infected, it does much more harm than the traditional virus," said Steve Morman, a NewsNet5 tech-support writer.

Symantec officials told NewsNet5 that the Love virus looks for those files -- including JPG and GIF type image and MP3 music files -- erases their contents and inserts its virus into the file instead. The virus then renamed your file with a ".vbs" extension at the end. For instance, "mypicture.gif" would become "mypicture.gif.vbs" after the virus attack.

Also affected are image files with the extension JPG and MP2 music files, as well as several types of technical files used by Windows such as "VBS" files.

Lesson re-learned: Make backup copies of important files, including images and songs.

In Asia, Dow Jones Newswires and The Asian Wall Street Journal were among the victims. "It crashed all the computers," said Daphne Ghesquiere, a Dow Jones spokeswoman in Hong Kong. "You get the message and the topic says 'ILOVEYOU,' and I was among the stupid ones to open it. I got about five at one time and I was suspicious, but one was from Dow Jones Newswires, so I opened it."

The virus was widespread in Europe as well. In Denmark, the parliament, telecom company Tele Danmark, channel TV2 and the Environment and Energy Ministry were all affected starting this morning.

Experts said they were stunned by the speed and wide reach of the virus -- which struck members of U.S. Congress and British parliament -- and warned computer users not to open the "LOVELETTER" attachment that comes with the contaminated e-mail.

"I have to tell you that, sadly, this affectionate greeting contains a virus which has immobilized the House's internal communication system," said Margaret Beckett, leader of Britain's House of Commons. "This means that no member can receive e-mails from outside, nor indeed can we communicate with each other by e-mail."

In the United States, the "love bug" shut down the Florida Lottery Web site and e-mail system, said lottery spokesman Leo DiBenigno.

U.S. Chamber of Commerce estimated 350,000 computers in the U.S. had been infected by 1 p.m. ET Thursday. The White House declined to give NewsNet5 an estimate of the extent of the attack.

CNN estimated the dollar value of the damage wreaked by the virus in the hundreds of millions as computer files were wrecked and business was lost, including from crashed financial networks and cash machines. ABC reported that U.S. State Department and military computers were infected.

In Pittsburgh, the zoo and main hospital reported problems ,while the airport and district attorney's office had to shut down their Internet connections.