Unwitting tweets send links to porn websites
Thousands of Twitter users have been hit by an attack which causes pop-up windows for pornographic sites to appear.
The bug, which appears as a message code, also sends a copy of itself to followers. It causes third-party websites to open by moving the mouse over a link.
Sarah Brown, Gordon's wife, apologised after unwittingly sending a tweet. She apologised to users, saying: "Don't touch the earlier tweet - this Twitter feed has something very odd going on! Sarah."
Experts said the bug could be used to display adverts.
"There is obviously the potential for cyber-criminals to redirect users to third-party websites containing malicious code, or for spam advertising pop-ups to be displayed," said security expert Graham Cluley of Sophos.
"It appears that in Sarah Brown's case her Twitter page has been messed with in an attempt to redirect visitors to a hardcore porn site based in Japan."
