A US district court in Texas has found Microsoft guilty of wilful infringement of two patents belonging to software maker VirnetX.
Microsoft has been ordered to pay $106m to VirnetX, which accused Microsoft in February 2007 of infringing the two patents relating to communications security.
According to court documents, Microsoft faced treble damages because the infringement was found to be wilful.
VirnetX, which claims to have built its patent portfolio from a US Central Intelligence Agency security project, expects Microsoft to appeal the decision, according to US reports.
The VirnetX victory comes less than a week after Microsoft lost an appeal in its dispute with i4i over XML support in Office 2003/2007.
The US Court of Appeals for the Federal Circuit upheld the lower court's decision in August 2009 that Microsoft willfully infringed i4i's patent.
Microsoft was forced to issue a 12.3Mbyte patch for Office 2007 to comply with a US court order banning the use of custom tagging after 10 January 2010.