Software giant Oracle is suing fierce rival SAP, accusing it of hacking into its computer network and stealing vital product information.
The business software is worth more than $60bn
Oracle claimed the German firm was guilty of "corporate theft on a grand scale" by gaining illegal access to one of its customer support websites.
Oracle and SAP compete in the business software sector, selling programs that help firms to be run more efficiently.
SAP said it would not comment until it had reviewed the 44-page lawsuit.
Oracle's lawsuit claims that SAP resorted to illegal activity to maintain its leadership in the market for business applications software.
It alleges that staff at TomorrowNow, a firm bought by SAP in 2005, accessed Oracle's computer network last year and illegally downloaded a wide range of copyrighted software and other material. The software was part of the Peoplesoft business that was bought by Oracle in 2005.
The PeopleSoft deal was one of a $20bn series of takeovers which Oracle has pulled off in the last three years, exerting greater pressure on market leader SAP.
Through its actions, TomorrowNow had assembled a "storehouse of stolen Oracle intellectual property", Oracle says.
"This theft appears to be an essential, and illegal, part of SAP's competitive strategy against Oracle," the complaint - lodged with a federal court in San Francisco - alleges.
SAP said it was still reviewing the detail of the lawsuit.
"Until we have a chance to study the allegations, SAP will follow its standard policy of not commenting on pending litigation," a spokesman said.
Oracle and SAP have been locked for years in the battle for the highly lucrative market for enterprise software.
In at times colourful language, executives of both companies have been trading barbs and difficult to verify claims and counterclaims of the number of customers won and lost.
During Oracle's acquisition spree and the resulting uncertainty in the market, SAP tried to lure customers by offering them a "safe passage" programme that would guarantee support for Oracle products with the help of companies like TomorrowNow.
SAP chief executive Henning Kagermann - speaking to the BBC News website hours before the lawsuit became public - said about 480 Oracle customers had made use of that programme.
He described it as a "good number, but not a huge thing," and argued that taking customers away from Oracle was "never part of our [expansion] strategy".
While SAP has managed to defend its market leadership in most areas, during the past six months the German company has performed below market expectations.
Oracle, meanwhile, appears to emerge from its takeover turmoil and recently posted better than expected results.