An unknown virus hit Kern Medical Center Tuesday, wreaking havoc for the last three days.

Fortunately, it wasn't the kind that infects humans. It infected computers.

Unfortunately, the computer virus is a particularly nasty strain that pushed KMC operations back to the paper age for most of Tuesday and continued, Thursday morning, to keep billing systems, mobile device access and administrative servers offline.

It downloaded "tons of porn documents" onto KMC computers and forced all hospital printers to spit out a stream of gibberish-covered paper, said hospital Chief Executive Officer Paul Hensler.

Kern Medical Center printers were unattended when the virus hit, Hensler said, and reams of paper were wasted.

The incident has landed Kern Medical Center in the middle of discussion at a one-day hospital cyber-terrorism conference being hosted at the University of California, Davis on Thursday by the Department of Homeland Security.

Special Agent Steve Dupre of the Sacramento office of the Federal Bureau of Investigation said Kern Medical Center's top internet technology leader has been tapped to speak about the attack at the conference.

"I spoke with the coordinator of next week's conference and he is very familiar with the hospital in your area. In fact, the CIO from that hospital is scheduled to be one of the presenters," Dupre wrote in an e-mail.

Dupre said the FBI cannot disclose information about other potential cases of cyber attacks against hospitals similar to the one at KMC "as those cases are still pending."

Kern Medical Center handled this week's cyber virus by isolating the problem and then systematically trying to eliminate it.

The hospital shifted to paper records Tuesday morning while technicians cut off the hospital's connection to the rest of the county computer network as a safety precaution and cleaned the virus out of critical patient-care systems, Hensler said.

Patient-care systems were back online by Tuesday evening, Hensler said. Internet access and desktop computers are now operational.

But the hospital's billing systems and administration servers -- the first areas hit -- remained offline Thursday morning. Hensler said they were expected to be up again Thursday evening.

There was some early concern that computer users in the Kern County Counsel's Office, who access KMC servers, might have exposed that office to the virus.

But that does not seem to be the case, Hensler said.

He said the virus was not designed to access and retrieve information from the hospital and patient records were not compromised.

"It's just a virus designed to disrupt our systems," Hensler said.

He said the hospital's McAfee virus protection software didn't catch the electronic infection because "McAfee didn't know about it."

Since then McAfee technicians have developed a way to purge the virus from Microsoft Word documents but are having a hard time finding something that will clear it out of image files.

Hensler said the FBI is aware of the situation at KMC.

"Some people put a lot of work into it," he said. "I doubt that they did this all for KMC."