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

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

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

The Love Bug e-mail appeared on computer screens in both houses of Congress in Washington and at the Pentagon.

The White House, Congress, the FBI and the Pentagon were all affected.

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

The "Love Bug": tempting to open

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.

The FBI have opened a criminal investigation. Reports suggest the virus may have originated in the Philippines. ISP Sky Internet Inc. in the Philippines are reported by ZDNet News to be hunting for a code writer who signed the virus code "Spyder, Manila, Philippines" and added the comment: "I hate go to school."

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.

Any one who opens the attachment triggers the virus, which automatically copies the same e-mail to everyone on the users address book.

The result is that systems are overloaded by the sheer volume of internet traffic, forcing them to crash or be closed down.

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.

Virus technologists at MessageLabs said that, while Melissa generated 200 copies of the virus in its first day, the Love Bug managed to infect 1,200 people in the first three hours.

"The virus has used every possible way to spread itself," said a Messagelabs spokesman.

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.

Europe, Asia hit

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

It's a particularly malicious virus

peoplesound.com director Andrew Fisher

"I have to tell you that, sadly, this affectionate greeting contains a virus which has immobilized the House's internal communication system," said British opposition Conservative Party spokesman, Sir George Young.

"This means that no member can receive e-mails from outside, nor indeed can we communicate with each other by e-mail."

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.