An eight-hour slowdown in worldwide Internet traffic at the weekend was caused by network delays at backbone ISPs Level 3 and Verio, according to Net traffic monitoring firm Keynote.

Users trying to access many top websites experienced "significant delays" as the normal near-100 percent site availability dipped to 93 percent, Keynote said.

Level 3's outage was caused by a configuration change to some of its edge routers in Chicago, which caused code to be corrupted elsewhere, said a source at the company.

This is the second network outage related to Level 3 this month. On 6 October, it cut off its peering relationship with Cogent, another large provider of Internet backbone bandwidth, over a financial dispute. That dispute was temporarily resolved and the peering connection was later re-established.

A spokesman for Verio denied that the service provider had suffered any outage. "The interruption displayed on the Keynote site was not due to a Verio outage. This was due, no doubt, to a connectivity issue with Keynote's probe."