11. Twitter

Date: May 7, 2012
Impact: Username and passwords of 58,978 Twitter accounts stolen

On Monday, May 7, 2012, an unidentified person took to Pastebin, a site that allows you to store text files, and dumped a ton of Twitter usernames and passwords. 58,978, to be exact. Twitter immediately downplayed the hack saying that a large majority of the compromised accounts were of spam and duplicate accounts. While that may be true, this the largest breach the young company has experienced.