On Friday, Symantec raised its Internet threat rating, citing confirmation of attacks using an unknown hole in Microsoft Word were being used to compromise computers on the Internet. The warning came as monitors at ISC detailed "limited targeted attacks," originating from China and Taiwan, against an unnamed company that used Word attachments to install Trojan horse programs on corporate networks.

Symantec warned subscribers to its DeepSight Threat Management Service that it had confirmed reports of active exploitation of a hole in Microsoft Word 2003. The attacks use Word document attachments in e-mail messages to trigger the security hole and run code that gives attackers control over vulnerable systems, Symantec said.

The hole caused Microsoft Word 2000 to crash but did not allow remote attackers to run "shell code" that can be used to control the machine following exploitation, Symantec said.

Few other details were available about the hole Friday, however. Symantec said that attacks using the Word hole were "limited" and "against select targets," according to a DeepSight alert message.

According to a post on the ISC's blog, the attacks are from China and Taiwan. ISC has traced communications from infected machines back to servers and Internet domains registered there. Text embedded in the malicious files are also written in Chinese, ISC said.