Missing flight simulator data probed in Malaysia Flight 370 disappearance.

Investigators looking at the flight simulator taken from the home of Malaysia Airlines Flight 370 Captain Zaharie Ahmad Shah have discovered that some data had been erased from it, Malaysia's acting transportation minister said Wednesday.

What the revelation means is unclear. It could be another dead end in an investigation that has been full of them so far, or it could provide further evidence for the theory that one or more of the flight crew may have been involved in the plane's disappearance 12 days ago.

"It's a thin lead, but it's a lead," former U.S. Federal Aviation Administration official Mary Schiavo told CNN.

Interim Transportation Secretary Hishammuddin Hussein didn't say what had been deleted, but simulation programs typically store data from previous sessions for later playback. He also did not say who might have deleted the data.

Photos: The search for Malaysia Airlines Flight 370

On the one hand, such files could reveal the simulator was used to practice diverting the plane and flying it to an unfamiliar airport, experts said.

But even if investigators retrieve past simulations showing that Zaharie practiced flying to seemingly odd locations, that doesn't necessarily indicate evidence of anything nefarious, Schiavo said.

"You put in strange airports and try to land there, just to see if you can do it," said Schiavo, adding that she sometimes does just that on the flight simulation program she has on her home computer.

One expert said deleting the files seemed odd. Desktop pilots don't usually delete such files because they are small and often kept to gauge progress, said Jay Leboff, owner of HotSeat, a simulator manufacturer.

"It would be suspicious to me, because there's no need to do it," he said.

Experts are examining the simulator in hopes of recovering the deleted data, Hishammuddin said. A law enforcement source told CNN on Wednesday that the Federal Bureau of Investigation is examining the hard drive.

If the files have not been overwritten by new data, retrieving them probably would be trivial for a computer expert, said Joseph Caruso, CEO of Global Digital Forensics. And even if they are, tools exist to help retrieve partial files that could be of use to investigators, he said.

The revelation came as the search for the missing airliner neared its 13th day.

Although the search area spans a vast area of nearly 3 million square miles, a U.S. government official familiar with the investigation said the plane is most likely somewhere on the southern end of the search area.

"This is an area out of normal shipping lanes, out of any commercial flight patterns, with few fishing boats, and there are no islands," the official said, warning that the search could well last "weeks and not days."

The official's comments echo earlier analysis by U.S. officials saying the most likely location for the missing aircraft is on the bottom of the Indian Ocean.

Australia said Wednesday that the area of the southern Indian Ocean where it is searching for the plane has been "significantly refined."

The new area is based on work done by the U.S. National Transportation Safety Board on "the fuel reserves of the aircraft and how far it could have flown," said John Young of the Australian Maritime Safety Authority.

But Australian ships and aircraft have so far seen nothing connected to the missing plane, Australian authorities said.

Angry families                                     

The lack of progress has angered and frustrated families, who have accused Malaysian officials of withholding information.

Some family members staged a protest at the hotel where media covering the search are staying.

"We have been here for 10 days, no single piece of information," one woman said. "We need media from the entire world (to) help us find our lost families, and find the MH370 plane."

Malaysian authorities appeared to hustle the women away.

In a statement, Hishammuddin said Malaysian authorities "regret the scenes at this afternoon's press conference."

"One can only imagine the anguish they are going through," he said of the families. "Malaysia is doing everything in its power to find MH370 and hopefully bring some degree of closure for those whose family members are missing."

An abrupt change in direction

The plane's disappearance continues to intrigue the public and frustrate officials, who have turned up no sign of the plane despite the involvement of teams from 26 nations.

On Tuesday, a law enforcement official told CNN that the aircraft's first major change of course -- an abrupt westward turn that took the plane off its route to China and back across the Malay Peninsula -- was almost certainly programmed by somebody in the cockpit.

The change was entered into the plane's system at least 12 minutes before a person in the cockpit, believed to be the co-pilot, signed off to air traffic controllers.

Some experts said the change in direction could have been part of an alternate flight plan programmed in advance in case of emergency; others suggested it could show something more nefarious was afoot.

But Hishammuddin said Wednesday that "there is no additional waypoint on MH370's documented flight plan, which depicts normal routing all the way to Beijing."

The Thai military, meanwhile, said it had spotted the plane turning west toward the Strait of Malacca early on March 8. That supports the analysis of Malaysian military radar that has the plane flying out over the Strait of Malacca and into the Indian Ocean.

But it didn't make it any clearer where the plane went next. Authorities say information from satellites suggests the plane kept flying for about six hours after it was last detected by Malaysian military radar.

How do passenger jets change flight paths?

Malaysian authorities, who are coordinating the search, say the available evidence suggests the missing plane flew off course in a deliberate act by someone who knew what they were doing.

Background checks

Investigators are looking into the background of all 239 passengers and crew members on board the plane, as well as its ground crew, Malaysian officials have said. They've received background checks on all nations with passengers on board with the exception of Russia and Ukraine, Hussein said.

So far, no information of significance has been found about any passengers, Hishammuddin said.

China says it has found nothing suspicious during background checks on its citizens on the flight -- a large majority of the plane's passengers.

Particular attention has focused on the pilot and first officer on Flight 370, but authorities are yet to come up with any evidence explaining why either of them would have taken the jetliner off course.

And some experts have warned against hastily jumping to conclusions about the role of the pilots.

"I've worked on many cases were the pilots were suspect, and it turned out to be a mechanical and horrible problem," said Schiavo, the former FAA official, who's also a CNN aviation analyst. "And I have a saying myself: Sometimes, an erratic flight path is heroism, not terrorism."