In the lawsuit, quietly filed two weeks ago in federal court in Los Angeles, ValueClick alleges that Tacoda's core business--profiling users based on their Web activity and serving them targeted ads--infringes on two patents dating back to the 1990s.

"We feel that we have a patent on the general principles of behavioral targeting, and that's what we're enforcing," said Scott Barlow, vice president and general counsel at ValueClick.

ValueClick has previously filed lawsuits against Blue Lithium and Revenue Science for infringing the same two patents. Both of those cases were settled; Blue Lithium was resolved last year, and the Revenue Science case was settled in February.

The lawsuit against Tacoda was filed several days before ValueClick announced the launch of its own new behavioral targeting platform.

One of the patents at issue, the 1998 "Method and Apparatus for Determining Behavioral Profile of a Computer User," involves creating psychographic profiles of Web users "by recording computer activity and viewing habits." The second, "Computer Program Apparatus for Determining Behavioral Profile of a Computer User," issued in 1999, likewise deals with creating behavioral profiles of Web users.

Both patents list Thomas Gerace as the inventor. Gerace founded Freedom of Information, Inc., which later became BeFree, Inc. and was acquired by ValueClick for $120 million in 2002. Gerace also is the founder and chief executive of the social networking site Gather.com.

In the lawsuit, ValueClick asserts that it informed Tacoda about the alleged infringement in March of 2007, or four months before Time Warner's AOL purchased the company for $275 million.

Tacoda, founded in 2001, has long been considered one of the pioneers of behavioral targeting. Clients include companies like The New York Times Co., which tapped Tacoda for behavioral targeting in 2004. AOL, which now owns Tacoda, declined to comment on the suit.

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