Computer users have been warned of a new virus which could spoil their Christmas.

The Scrooge-like virus, called W97M/Prilissa, acts in a similar way to a previous scourge, Melissa, which attached itself to the Microsoft Outlook e-mail program and spread to other users by sending e-mails to the first 50 addresses. Melissa caused harm by clogging up e-mail servers, but the latest virus is more damaging to a computer's hard drive.

Prilissa is timed to infect a user's C drive on Christmas Day, delivering a message when the machine is turned on, reading: ". . . You dare rise against me . . . the human era is over . . . the CyberNet era has come."

The virus will only affect users of Windows 95 or 98 and those running Microsoft Outlook software. It is contained within a Word 97 file and comes with the e-mail subject header: "This document is very important; you've got to read this."

Reports that home users will be the biggest group to be hit, as many offices in Britain and the Republic will be closed during the Christmas period.

Chief researcher at Symantec Anti-Virus Research Centre Mr Eric Chien said: "People need to become more aware of virus attachments on e-mails and practise safe computing. Basically, do not open anything that you were not expecting, and get anti-virus software."

The Prilissa virus can easily be detected and removed from a machine by running commonly available software.