Compuware lawyer Daniel Johnson Jr told the jury in the US District Court in Detroit: This is about IBM, one of the largest corporations in the world, going out and embarking on a plan to kill Compuware.

This case is really simple, said Johnson. This is about the theft of technology worth millions and millions of dollars. Johnson also presented jurors with an IBM memo apparently titled Compuware Killer, which allegedly set out its plan to compete with and subsequently destroy Compuware.

He claimed that IBM hired ex-Compuware developers to build its new range of mainframe software tools, even though those employees had signed confidentiality agreements.

IBM stands accused by Compuware of stealing its trade secrets, specifically claiming IBM stole trade secrets to copy two of its programs, a mainframe-based file manager and a program that helps users locate the source of problems on their mainframes.

Compuware alleges that IBM then heavily discounted the products or gave them away free as part of hardware deals in order to kill off the main competitor in the mainframe management market: Compuware.

IBM denies the charges, its attorneys arguing that it only used public information and its own skills to develop its mainframe software products. It says Compuware’s case is simply an attempt to block competition.

IBM lawyer Evan Chesler said that the two companies’ software is similar not because IBM stole Compuware’s trade secrets, but simply because they are both designed to work with IBM mainframes.

IBM also hit back by claiming that it had helped Compuware to develop its mainframe products in the first place, and that Compuware’s programs actually contain lines of IBM source code. The case continues this week.

It is a clear case of David against Goliath: Compuware’s latest annual revenue was just $1.2bn, compared to IBM’s $96.5bn. IBM is also embroiled in a long-running legal dispute over claims that it breached its contract with SCO Group Inc, by contributing Unix code to the Linux operating system.