Apple has been ordered to pay $625.6 million (£428 million) after a federal jury in East Texas ruled that services such as FaceTime and iMessage infringed on technology patents held by Nevada patent-holding company VirnetX.
VirnetX had previously won a $368 million (£252 million) verdict against Apple on similar claims in 2012. That award was overturned by an appellate court, which ordered a new trial.
While an attorney for VirnetX praised the verdict, Apple vowed to appeal and said the case shows a need for patent-system reform.
Apple Inc has won appeals in similar cases after losing in East Texas, which is known for large judgments in patent claims.
VirnetX is a company that buys technology patents and aims to make money from licensing fees and lawsuits. It has previously sued Microsoft, Cisco and others.