SAN FRANCISCO --- YouTube co-founder Steve Chen once warned a fellow co-founder to stop posting pirated videos on their Web site, according to court documents unsealed Thursday as part of a 3-year-old copyright lawsuit against the online video leader.

That bit of intrigue was among the confidential information that had been kept under wraps since Viacom Inc. sued YouTube for alleged copyright infringement of The Colbert Report, The Daily Show and other shows in a federal court in New York.

The newly released evidence also revealed that Viacom wanted to buy YouTube before getting beat out by Google Inc., which acquired the site for $1.76 billion in 2006. One Viacom executive even suggested a joint bid by Viacom and Google.

Viacom, the owner of Paramount Pictures and cable TV channels that include Comedy Central, sued YouTube in 2007 seeking more than $1 billion in damages.

The media company alleges that YouTube allowed copyright-protected clips to appear on its Web site in its early days to attract a bigger audience. YouTube maintains it has always obeyed the Internet's copyright laws.

An e-mail exchange less than six months after YouTube's February 2005 inception showed that Chen was worried Jawed Karim's lax attitude toward copyrights might cause trouble.

"Jawed, please stop putting stolen videos on the site," Chen wrote in the July 19, 2005, e-mail.

In a statement after the documents were unsealed, YouTube said Chen's e-mail was referring to some aviation videos that had been making the rounds on the Web.

Karim left YouTube before Google bought it in 2006.