The virus was activated when computer-users opened the file, prompting their machines to send the infected file to every contact in their address lists.

The "Love Bug": tempting to open

This created a huge volume of electronic mail that overwhelmed computer systems.

Copycat viruses, able to elude anti-virus software designed to block "I love you" messages, are reported to have followed within hours.

Some users reported receiving the same e-mail, but one that replaced the "I love you" wording with "very funny joke".

Experts say more are likely to follow.

Philippines lead

Reports suggest the Love Bug may have originated in the Philippines.

The internet service provider Sky Internet Inc. in the Philippines is reported by ZDNet News to be hunting for the author who signed the virus code "Spyder, Manila, Philippines" and added the comment: "I hate go to school."

Tackling the virus

Do not open it Delete it using shift del As with all e-mails, if in doubt do not run any attachments you are not expecting If you have run the attachment, isolate your machine from any network and phone your help desk or seek expert advice Remember to keep your anti-virus software up-to-date and be vigilant about attachments

Analysts estimate hundreds of millions of dollars of damage has been caused in the US, the most computer-dependent country in the world.

Computer security firm Trend Micro estimated at 1915GMT on Thursday that some 1.27 million computer files were infected worldwide, with nearly 1million in the US.

The State Department was forced to disconnect its computer systems from the internet, according to a spokesman.

US companies were likewise forced to take their e-mail systems off-line to isolate the spread of the virus and it was blamed for shutting down the web site, the state lottery in Florida.

It spread at great speed. One DJ in Texas received the e-mail virus 1,500 times.

Europe was also hard hit on Thursday. Among the victims were the UK House of Commons, the Danish parliament and the Swiss federal government computer networks, along with many banks and other companies.

About 10% of businesses around the UK are believed to have been affected.

In Asia, Dow Jones Newswires and the Asian Wall Street Journal were among the victims.

Delete

Computer experts advise people using Microsoft Outlook who receive the e-mail not to open it, but to shift-delete it immediately.

If the message is opened, users should on no account open the attachment that comes with it.

It crashed all the computers

Dow Jones, Hong Kong

If the attachment is opened, experts advise users to log off, switch off the computer, and contact their help desk.

The virus, identified as a "worm", spreads in the same way as the Melissa virus, which last year infected about one million computers, clogging whole networks in the United States and causing $80 million in damage.

Experts say the Love Bug is much more serious than Melissa as it overwrites audio and picture files, replacing them with its own code. The virus is reactivated if one of these files is subsequently opened.