Last year, Cisco Systems sued a security researcher and organizers of the Black Hat event after a presentation on switch and router security. This year, Cisco is quietly investigating a possible flaw that was mentioned during a talk on VoIP.

In a presentation Wednesday at Black Hat in Las Vegas, Hendrik Scholz of Germany's Freenet Cityline briefly mentioned a flaw in Cisco software, Black Hat organizers said. This flaw had apparently not been patched. Scholz and Black Hat are now keeping quiet on the issue to give Cisco time to investigate and respond.

"We are looking into it," said John Noh, a Cisco spokesman. "We have to look at the validity of it. We take these things very seriously. And if we need to inform our customers, we will."

It is unclear exactly what Cisco application the alleged flaw is in, but it appears to be related to voice over Internet Protocol applications since Scholz's talk was on "SIP Stack Fingerprinting and Stack Difference Attacks." Most of Cisco's current products don't yet offer extensive SIP, or Session Initiation Protocol, support.

This year, Cisco is playing nice. The company is one of the main Black Hat sponsors and Chief Security Officer John Stewart is in attendance. Cisco on Wednesday also threw a party for Black Hat attendees at Pure, the night club at Caesars Palace. One of the attendees spotted at the party: Michael Lynn.

Looks like Cisco learned a lesson after all.