A sophisticated group of hackers believed to be associated with the Chinese government, who for years targeted U.S experts on Asian geopolitical matters, suddenly began breaching computers of experts on Iraq as the rebellion there escalated, a security firm said Monday.

CrowdStrike Inc. said that the group is one of the most sophisticated of the 30 it tracks in China and that its operations are better hidden than many attributed to military and other government units.

CrowdStrike co-founder Dmitri Alperovitch said he has "great confidence" the hackers are affiliated with the government, though he declined to provide many details on the matter. A spokesman for the Chinese Embassy in Washington could not be reached for comment.