the instigate for of the hack as retaliation for the controversial film. tonight, the fbi is scrubbing sony's computer system, trying to gather enough evidence to definitively point a finger at the hacking culprit. >> it's a complex new wants investigation and it involves not just going into your own i.t. systems but hackers have gone through multiple, multiple infrastructures to get to where they have gotten to. so it's not something that sony is going to solve in a day or a week or a month. >> reporter: it's had a devastating effect on the entertainment company revealing personal information of employees and fallacious e-mail exchanges of a-list celebrities. u.s. law enforcement sources say they believe they were penetrating their computer system as early as this past summer but it wasn't until later the company reported it to authorities who began investigating in november. and today, former employees of