The patches, released Friday, mark Siemens' first response to a high-profile computer security incident since the Stuxnet worm, which was discovered a year ago circulating on computer networks in Iran.

Siemens fixed a pair of flaws in the S7-1200 controller, acknowledging that one could be leveraged to take control of the system using what's known as a replay attack. A second flaw, in a Web server that ships with the device, could give attackers a way to crash the system. However, the attacker would have to first find a way onto the victim's network before launching these attacks.

Siemens had been scrambling to fix the bugs since they were discovered earlier this year by Dillon Beresford, a researcher with security vendor NSS Labs. Beresford had hoped to discuss the issues at a May hacking conference in Dallas, but when it became clear that Siemens could not fix the problem in time.

His company said that talking about the bugs was too risky and decided instead to .

In an interview Friday, Beresford said it wasn't clear how many of the six vulnerabilities he'd discovered had been patched. That will require further testing. He said the replay attack that Siemens patched Friday is one of the most serious of the bugs, but there is at least one other equally serious problem that may not yet be fixed.