Apple Inc. announced on Friday that it filed a countersuit against Nokia Corp, claiming that the Finnish cellphone maker is infringing 13 Apple technology patents.

Nearly two months ago, Nokia sued Apple, claiming that it had spent $60 billion developing the technology covering the infringing patents.

Apple has now countersued Nokia and claimed it has infringed 13 of its patents.

Apple General Counsel Bruce Sewell said, Other companies must compete with us by inventing their own technologies, not just by stealing ours.

Countersuits are a staple of patent litigation, which often ends in cross-licensing agreements.

Apple shares fell 56 cents to $195.81, while Nokia's stock rose 24 cents a share to $12.80 in late morning trading.

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