Gipson Hoffman & Pancione, which is representing Cybersitter in a $2.2 billion piracy suit filed against China and seven major computer manufacturers, said in a statement that its attorneys were sent customized Trojan emails aimed at retrieving data from the company's computers and servers.
It said the specific source of the attacks had not been determined, but they appeared to have been initiated in China.
Cybersitter has accused the makers of China's controversial Green Dam Internet filtering software of illegally copying over 3,000 lines of code from its own filtering program.
It said PC makers including Sony Corp, Lenovo Group, Toshiba Corp, Acer and Asustek had continued to distribute the software even after becoming aware that the code had been stolen.
China announced in the middle of last year that all PCs sold in the country would be forced to carry the Green Dam software, but by July, after protests by human rights groups and lobbying by PC makers, it had abandoned the plan.
Google said on Tuesday that it was considering closing down its Chinese site after being subject to a phishing campaign aimed at accessing the Google mail accounts of Chinese human rights activists.
It said at least 20 other companies had been hit in a series of similar attacks originating in China.
Adobe Systems, which makes the popular Acrobat, Flash and Photoshop software, said on Wednesday that its network systems had also been targeted.
(Reporting by David Stanway, Editing by Chris Lewis)