The reason for the lawsuit is the illicit and faulty copy of Assassin’s Creed.
The suit filed against Optical Experts Manufacturing lists copyright infringement, breach of contract and negligence. The reason for this is that Ubisoft wants to have learned that the pirated version of Assassin's Creed that was available on the internet more than a month before the game officially hit the shelves, originated from OEM. An employee of the company is supposed to have taken a copy home to publish it online. Therefore Ubisoft sues the company for not fulfilling parts of the contract made. The publisher claims that Assassin's Creed has been downloaded more than 700,000 times while in June only 40,000 copies o the game were sold.
Another accusation made by Ubisoft is that their reputation has been harmed, since the illicit version of the game had been review multiple times and often got low marks since a bug was integrated which caused the game to crash.