Prime Minister Tony Blair and his official website are the target of a new internet worm.
The worm accuses Mr Blair of wasting money
The Quaters worm spreads via e-mail and by internet chat systems and only affects Windows computers.
It carries a message accusing Mr Blair of wasting money on illegal immigrants instead of spending it on schools and the health service.
But anti-virus experts say the risk from the worm is low as they have only had few reports of infected computers.
This is not the first time someone has tried to use a computer virus to express their political views.
Previous worms have tackled the frictions between India and Pakistan, while others have been directed at leaders such as Bill Clinton and Margaret Thatcher.
"Tony Blair is having enough problems with his chief spin doctor resigning and the Hutton Inquiry, without having an axe-grinding British virus writer causing mischief too," said Graham Cluley, senior technology consultant with the Sophos anti-virus firm.
The Quaters worm overwrites files on an infected computer with the text "Infected by the WIN32.SORT-IT-OUT-BLAIR Virus!"
It may then try to knock out the Downing Street website, www.number-10.gov.uk.
Asked about the worm and the potential attack on the website, Downing Street said it had no comment to make on the matter.
The first a computer user may know about worm is when it displays a message critical of Mr Blair.
"Dear Tony Blair, Why are you spending all our taxes on illegal immigrants!?! How about you stop worrying about other countries and worry about ours???" says the message.
It ends with a warning for the prime minister: "Think about it Mr Blair. Your career depends on it. We've had enough."
The worm can spread via e-mail using a variety of subject lines, such as Your Account Information. It also uses internet chat relay systems, posing as an attempt to break a net chain mail world record.
But it seems unlikely to cause too many problems for computer users, with anti-virus firms classifying Quaters as a low-risk worm.