Security software maker Symantec is taking legal action against Microsoft, accusing it of misusing its technology.
Symantec is best known for its Norton Antivirus software
The action, filed in a US federal court in Seattle, alleges that Microsoft improperly used Symantec's data storage techniques in its own software.
Symantec wants compensation, saying the alleged infringement amounts to misappropriation of its trade secrets.
Microsoft describes the accusation as unfounded and says it has tried unsuccessfully to resolve the issue.
The disagreement is based on Symantec's Volume Manager software, which allows operating systems to store and handle large amounts of data.
Symantec believes Microsoft has "deliberately and surreptitiously misappropriated" the technology "and thereby convinced the US government to issue patents to Microsoft based on technologies invented by Symantec".
For its part, Microsoft says it licensed the technology from Veritas Software, a company that Symantec acquired last year in a $13.5bn (£7bn) deal.
"We are confident that our actions are wholly consistent with the legal agreements between Veritas and Microsoft and that these claims will be shown to be without merit," Microsoft said in a written statement.
Symantec produces Norton software, a package used to protect computers from being hacked into.
The news comes as Microsoft intends to launch its own internet security software.