A US International Trade Commission judge has ruled that Redmond used technology in its mobile phones without permission.
On the plus side, Judge Theodore Essex, said that while Microsoft infringed two wireless cellular patents owned by InterDigital it would not be against the public interest to ban the Microsoft devices from being imported into the United States.
The judge's decision must be reviewed by the full commission before any import ban is enacted.
InterDigital first accused Nokia of infringing its patents in 2007. Microsoft acquired Nokia's handset division last year. The InterDigital patents relate to moderating a mobile phone's power to reduce signal interference.
The ITC originally cleared Nokia of infringement, but in 2012 the US Court of Appeals for the Federal Circuit, the nation's top patent court, overturned that decision and sent it back.
Microsoft said that the fight was not over yet and it had a successful track record challenging patent assertion entities that misuse industry standards.
InterDigital Executive Vice President Lawrence Shay said the company looks forward to "continued discussion" with Microsoft to license its patents.