TAIPEI – Acer Inc. has countersued Hewlett-Packard, alleging violation of four patents, the PC maker said today.

H-P, the world's top PC maker, sued Acer in March for patent infringement in an attempt to block its rival from selling certain products in the U.S.

The move touched off a series of subsequent lawsuits in which Acer alleged three of its contract assemblers, Quanta Computer, Foxconn and Wistron Corp., were partially to blame.

Quanta, Foxconn and Wistron also produce PCs for H-P. Adding to the intrigue, Wistron is the former EMS arm of Acer.

Acer is the world's fourth largest PC maker, and has been gaining ground in recent quarters.