Everyone has a theory about who really hacked Sony Pictures Entertainment Inc.

Despite President Barack Obama’s conclusion that North Korea was the culprit, the Internet’s newest game of whodunit continues. Top theories include disgruntled Sony insiders, hired hackers, other foreign governments or Internet hooligans. Even some experts are undecided, with questions about why the communist state would steal and leak gigabytes of data, email threats to some Sony employees and their families and then threaten moviegoers who planned to watch "The Interview" on Christmas.

"Somebody’s done it. And right now this knowledge is known to God and whoever did it," said Martin Libicki, a cyber-security expert at RAND in Arlington, Virginia, who thinks it probably was North Korea. "So we gather up a lot of evidence, and the evidence that the FBI has shown so far doesn’t allow one to distinguish between somebody who is North Korea and somebody who wants to look like North Korea."

Perhaps the only point of agreement among those guessing is that even the most dramatic cybercrimes can be really, really hard to solve convincingly. When corporations are breached, investigators seldom focus on attributing the crime because their priority is assessing damage and preventing it from happening again.

"Attribution is a very hard game to play," said Mike Fey, president of security company Blue Coat Systems Inc. and former chief technology officer at McAfee Inc. "Like any criminal activity, how they get away with it is a very early step in the planning process, and framing another organization or individual is a great way to get away with something.

Fey added: "If they’re smart enough and capable enough to commit a high profile attack, they’re very often smart enough and capable enough to masquerade as someone else. It can be very difficult to find that true smoking gun."

In a report earlier this month, Fey’s company described a malicious software tool called Inception, in which attackers suggested a link to China, used home routers in South Korea, included comments in Hindi, with text in Arabic, the words "God_Save_The_Queen" in another string, and used other techniques to show links to the United States, Ukraine or Russia.

Unlike crimes in the physical world, forensic investigators in the cyberworld can’t dust for fingerprints or corroborate evidence by interviewing suspects. In prior closed-book cases, cybercriminals caught bragging online were only charged after evidence was found on their hard drives.

"The NSA (National Security Agency) has penetrated a lot of computers, but until Edward Snowden came around, nobody was certain because the NSA has the world’s best operational security. They know how to cover their tracks and fingerprints very well," Libicki said.