Acer has counter-sued Hewlett-Packard for patent infringement, as the two companies continue to fight for more of the global PC market.

Acer, the world's third-largest PC vendor, filed counter-claims in a Wisconsin court and with the US International Trade Commission, alleging that HP, the world's largest PC vendor, infringed on patents related to PCs, servers and peripherals.

Acer will take all necessary steps to protect and enforce its patented technologies, with or without a legal proceeding, Acer said in a statement. An HP spokeswoman said the company has no comment.

HP sued Acer in March for allegedly selling PC products that infringe on patents related to optical drives, clock frequency switching and power consumption. HP sued again in April, alleging infringement of PC patents related to power savings, heat management, regulating the flow of data and improving screen picture quality.

Acer vowed to strike back when chairman J T Wang announced in April that the company had retained intellectual-property lawyer Chris Ottenweller of Orrick, Herrington & Sutcliffe for its defence. Acer in July filed a counter-claim against HP's two lawsuits, alleging HP infringed its antenna and DVD-ROM head technology patents.

The lawsuits come as Acer increases its US and global presence at a brisk rate. The company extended its lead over Lenovo as the world's third largest PC vendor with the recent acquisitions of Gateway and Packard Bell. During the third quarter, Acer recorded a 59.2 percent increase from the previous year in global PC shipments, drawing closer to HP, which recorded a 19.6 percent increase, according to an IDC survey.