Hackers over the weekend accessed Microsoft's YouTube channel to swap out videos with their own. It is unclear what the intruders' motive was, but they may have been able to access the account by stealing its login credentials from a Microsoft employee, Graham Cluley, senior technology consultant at anti-virus firm Sophos, said in a blog post Sunday. One of the unauthorized videos posted was titled “Bingo” and featured an animated video game character shooting another character. By Monday morning, the channel was operating normally. The incident followed hackers last week taking over the Sesame Street YouTube channel to display pornographic videos.