According to news.yahoo, the previously confidential information was released as evidence in a copyright infringement lawsuit Viacom filed against YouTube in 2007.
In one email exchange among YouTube co-founders Chad Hurley, Steve Chen and Jawed Karim, there appeared to be in-house copyright abuses.
"Jawed, please stop putting stolen videos on the site," Chen wrote in the July 19, 2005, email. "We're going to have a tough time defending the fact that we're not liable for the copyrighted material on the site because we didn't put it up when one of the co-founders is blatantly stealing content from other sites and trying to get everyone to see it."
In a statement after the documents were unsealed, YouTube said Chen's email was referring to some aviation videos that had been making the rounds on the Internet. "The exchange has nothing to do with supposed piracy of media content," YouTube said.
The documents were released because both companies are trying to persuade the judge to decide the case without going to trial.
According to records, Viacom wanted to buy YouTube at least seven months before it filed its lawsuit and often used the site to promote the shows on its cable TV stations.
Google ended up buying YouTube in 2006 and offered to pay Viacom $590 million for licensing rights to video. Instead, Viacom sued Google for $1 billion in damages, claiming that YouTube allowed protected video clips to appear on its site.
YouTube claimed it has always followed online copyright laws.