While details of the flaw are unclear, it is apparently widespread and affects much of the network infrastructure used by the major Internet service providers, CNET News.com learned Wednesday. Cisco is a major provider of network switches and routers used to direct data across the Internet.

Cisco could not immediately comment, but telecommunications provider Sprint confirmed that there is a problem.

"Sprint is aware of the issue regarding Cisco," said spokesman Charles Fleckenstein, reading from a statement. "Modifications are being performed on the Sprint Internet backbone, and customers should have no concerns regarding an interruption of service in regards to Sprint."

The flaw could be used by an attacker to crash a router, clogging the Internet's communications channels, sources said. Due to the vulnerability's nature, the router won't appear to be down, said one network expert familiar with the flaw. The router would have to be restarted or reset to make it operational.

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