Microsoft has lost a patent case against telecoms company Alcatel-Lucent.
The computing giant had accused Alcatel-Lucent of infringing patents business telephone network technologies.
In particular, it pointed to four patents for the software in a system that integrates telephones with computers for calls, messages and videoconferences.
But now the US International Trade Commission has thrown out the complaint and said that there was no violation.
Initially, a judge had found Alcatel-Lucent guilty of infringing one patent but this latest ruling goes back on that.
"We are pleased with the ITC's decision and had always believed that we had a strong case", said Alcatel-Lucent spokeswoman Mary Ward.
Microsoft, however, is disappointed.