The malicious software used to steal information from companies such as Google contains code that links it to China, a security researcher said TuesdayAfter examining the back-door Hydraq Trojan used in the hack, SecureWorks researcher Joe Stewart found that it used an unusual algorithm to check for data corruption when it transmits information. The source code for this algorithm, "only seems to be found on Chinese Web sites, which suggests that the person who wrote it reads Chinese," Stewart said.That may be an important hint. Because while Google has implied that the people who hacked its computers had the support of the People's Republic of China, company executives have admitted that they have no proof.Google has threatened to pull out of China, in part because of the cyber attack.According to Stewart's firm, aside from the fact that the fact that some of the servers used in the attack were hosted in China, there had previously been no evidence of a China link. Because the attackers could have simply purchased or hacked into hosting services in China, linking the command-and-control servers to China is inconclusive. The code behind the attack, called Aurora, was written in 2006. But, apparently it was rarely used, which helped it evade antivirus detection for several years. The Hydraq Trojan -- just one element of all of the Aurora software security firms have found -- dates back to April 2009, Stewart said. Google learned of the attack in December, and quickly notified other affected companies.Like other Trojans, Hydraq gives the attackers ways of running commands on the computes they hack. With it they can do things such as list directories, and read and search files, Stewart said.Stewart, who earns his living analyzing malicious code says he has never seen this particular data-checking algorithm used anywhere else except with Hydraq.Whomever is behind Aurora is known to have hit 34 companies, but researchers suspect that there may be many more victims.