In a new twist in the lawsuit that accuses Apple of resorting to unfair tactics to maintain its dominance in the digital music business, the court was informed that the company deleted songs that iPod users had downloaded from rival music services between 2007 and 2009, according to a Wall Street Journal report.

According to plaintiff attorney Patrick Coughlin, whenever users tried to sync their iPod to their iTunes library after downloading music from a competing service like Real Networks’ music store, they would receive an error message instructing them to restore the factory settings. In doing so, the music from rival services would disappear.

Apple directed the system “not to tell users the problem,” Coughlin said.

Defending the practice, Apple security director Augustin Farrugia said that presenting too much information to users would have confused them, something the company didn't want. He told the court that updates that deleted non-Apple music files were aimed at protecting users from hackers and malicious content.

Filed in 2005 by Thomas Slattery, the lawsuit alleges that Apple violated federal antitrust laws as well as California's unfair competition law by not allowing music purchased on the iTunes Music Store from being played on devices other than iPods, and by restricting iPods to play music purchased from other digital music services.

The trial is expected to see Apple marketing head Phil Schiller and iTunes chief Eddy Cue testify during the court proceedings this week, while portions of a video deposition of Steve Jobs are also expected to be played.