Experts note that there are also several other possible causes of the crash of one Washington Metropolitan Area Transit Authority (WMATA) train into another with such force that the first literally climbed on top of the other. They could include track problems, mechanical failures and .

But the WMATA computer systems are likely to get significant attention from investigators because they were designed to prevent such rear-end accidents. The computer systems are constantly making decisions on train speed based on track-bed sensors that monitor train movements.

Kegan Kawano, a senior security consultant at Industrial Defender Inc. in Foxboro, Mass., noted that NTSB investigators likely have to rule out whether the crash resulted from a misconfigured control system, a physical computer failure or a security breach.

Security breaches aren't unknown in transportation systems. Kawano said he's aware of 10 security incidents in transit systems since about 2003. Among them, in 2007, a Polish teen allegedly derailed a train by hacking into a network. In 2003, a widely disbursed used by rail hauler CSX Corp., causing it to halt some passenger and freight service, he added.

Kawano did note that rail automation systems are so unique that hackers oftentimes can't figure out how to penetrate them. "They are systems that rely on known technology but are put together in unique ways," he said.