Associated Press news agency's Twitter feed is hacked
24 April 2013 Last updated at 06:45 BST
A fake tweet claiming President Barack Obama had been injured in an explosion at the White House has been sent from the Twitter account of the Associated Press news agency.
It spread ripples of alarm through US markets, and the Dow Jones Industrial Average dropped 150 points as it was retweeted.
The White house was quick to clarify that the US president was fine and no explosions had occurred. The hacked account has since been suspended.
Dr Herb Lin, a cyber security expert, explains how media agencies are likely to make security changes to their Twitter accounts.