Symantec has admitted flaws in some of its anti-virus products could allow malicious hackers to use denial of service (DoS) attacks to crash systems.

On Monday, the company posted a notice on its website that described two DoS vulnerabilities in the 2004 and 2005 editions of Symantec Norton Antivirus, Norton Internet Security and Norton System Works.

The company has patched the holes and distributed software updates to users of the LiveUpdate automatic update service. However, systems that are not patched could be susceptible to remote attack through e-mail or the Web, Symantec said.

The holes were discovered by security researchers in Japan. In one case, the Information-Technology Promotion Agency-Japan (IPA) discovered a problem on systems running Norton Antivirus 2005 with the Auto-Protect and SmartScan features enabled. Auto-Protect is a feature that scans files sent from the Internet, removable disks or e-mail attachments and looks for viruses, Trojan horse programs and other malicious code. SmartScan allows Norton Antivirus to quickly scan specific types of files often associated with malicious code, such as exe and doc files.

With SmartScan enabled, researchers at IPA found that renaming a file on a shared network folder can cause the system running Norton Antivirus to crash.

In a second issue reported by the Japan Computer Emergency Response Team (JPCERT), machines running Norton AntiVirus 2004 and 2005 crashed when Auto-Protect scanned a specific type of file that Symantec declined to identify.

Symantec rated the two holes "low" risks and said the company is unaware of any adverse customer impact from the vulnerabilities. Still, customers were advised to run LiveUpdate for any affected products until all available product updates are downloaded and installed.

The news comes amid numerous reports of flaws in anti-virus products, which many Internet users rely on as protection against wider Internet security threats.

In February, Symantec issued patches to fix a high-impact hole that affected almost its entire product line. On 17 March, another warning about a remotely exploitable hole in anti-virus technology from Symantec's chief competitor, McAfee, was released.