HTC's action was expected after Apple filed a patent infringement suit against the company in March. Back then Apple CEO Steve Jobs had said: "We can sit by and watch competitors steal our patented inventions, or we can do something about it. We've decided to do something about it," said Steve Jobs, Apple's CEO. "We think competition is healthy, but competitors should create their own original technology, not steal ours."
Apple's move against HTC was seen as a proxy for an attack on Google, since HTC makes smartphones based on Google's Android software, which has gained ground on Apple's popular iPhone.
Apple has also sued Nokia in late last year, responding to a lawsuit brought earlier against the company by Nokia. Apple claims that Nokia is infringing 13 Apple patents.
Nokia's lawsuit, filed in October, claimed that Apple infringed on 10 of its patents covering both phone calls and Wi-Fi access.
Both suits were filed in federal court in Delaware.