It looks like WordPress.org was hacked and backdoors were added to some plugins.
Malicious software downloads invade WordPress • The Register
They found malicious code in AddThis, WPtouch and W3 Total Cache.
If you recently updated these plugins, you will need to reinstall them with new copies.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin