Cisco dominates the router market

It follows a warning from the California-based company about a problem in the software used in its routers, a device that decides how and where to send internet traffic.

The flaw could allow attackers to take control of the hardware and block access to websites.

Cisco has released a patch for the vulnerability, saying that it had no reports of anyone exploiting the flaw to attack its routers.

Liable to crash

The danger to the routers is due to the way the Cisco equipment deals with some internet data.

By sending a special sequence of data, a malicious hacker could trick the router into believing it was full, causing it to crash.

"Cisco IOS [software] is a very widely deployed network operating system," said the net security watchdog, the Computer Emergency Response Team (Cert).

"A vulnerability in IOS could allow an intruder to execute a denial-of-service attack against an affected device."

Technicians at internet service providers have been rushing to plug the hole, which in theory could bring net traffic via their networks to a halt.

Cisco released a fix for the software problem late on Wednesday, which can be downloaded from its site.

A company spokesman said they had had no reports that any of their customers had been affected by the vulnerability.

Cisco is the world's largest supplier of router equipment. Analysts Gartner estimate that the company has 55% of the service provider router market.