The virus, unleashed on Friday afternoon has reached Britain after bringing almost 60 major companies and organisations in the US to a halt.
Employees have been warned not to open any emails but experts say the bug has already infected more than 60,000 computers at one British firm.
Once Melissa is opened, it finds the email address book and sends itself to the first 50 names. To the embarrassment of the computer users, the message is a list of hard-core porn sites that appears to come with the sender's recommendation.
The email containing the virus gives its subject as an 'important message from' followed by the name of the sender. The message reads: 'Here is that document you asked for ... and don't show it to anyone else.' A document called list.doc is attached. Opening the email is harmless. But opening the document unleashes the virus, which is believed to affect only the email programme Microsoft Outlook.
The virus receieved its name because it leaves a change on the registry file including the words 'Melissa? ... by Kwyjibo.'