Last night, an individual started spreading fake rumors of Steve Jobs suffering from a heart attack. The story was posted to CNN's iReport "unedited" and "unfiltered" citizen journalism site and subsequently submitted to Digg.com.
The Digg story then gained attention on 4chan, an unmoderated discussion board, which then proceeded to promote the story as a prank. 4chan most recently gained (even further) notoriety as the discussion forum where vice presidential candidate Sarah Palin's email account contents and password were posted.
Apple's stock took a brief dip this morning based on the rumors. An Apple spokesperson has confirmed that the rumor is "not true".
Update: The SEC is investigating to see if this was intentional stock manipulation.