(Bloomberg) — Sony Corp.'s computer network was hacked in whatmay be a blackmail attempt, according to a person with knowledge ofthe matter.

The breach of the entertainment and electronicscompany's systems is under investigation, said the person, whowasn't authorized to speak publicly and asked not to be named. In astatement, Sony said it was investigating “an IT matter.”

The incident began when a picture of a skull appeared on companycomputer screens, the entertainment website Deadline.com reportedyesterday. The image was accompanied by a message that read Sonyhad been hacked by #GOP and that private data would bereleased at 6 p.m. New York time yesterday if its undiscloseddemands weren't met.

The hack is being linked to a group called “Guardians of Peace,”the person said.

Masaki Tsukakoshi, a Tokyo-based Sony spokesman, said that bothSony Computer Entertainment Inc. and the PlayStation Network wereoperating as normal without any disturbances.

Many large global companies have fallen prey to computerhackers. JPMorgan Chase & Co, Home Depot Inc. and Target Corp.have all been subject to hacks.

In the case of JPMorgan, hackers earlier this yearaccessed data on 76 million households and 7 millionsmall businesses. This month, Home Depot said 53 million e-mailaddresses were taken, in addition to the 56 million payment cardsthat were previously disclosed.

Earlier Attacks

Shares of Sony rose 6.1% to 2,582.5 yen at the close of trade inTokyo, the highest since April 2011. The stock has gained 41% thisyear compared with an 8.2% rise in the Topix index.

PlayStation Network and Sony Entertainment Network, which enablegamers to play each other and access content, were taken off lineby a so-called distributed denial of service attack, theTokyo-based company said in August. At the time, the company saidit had no evidence that personal information was accessed bycomputer hackers who drove artificially high traffic to Sonyservers, it said.

In 2011, Sony's online-entertainment service was attacked byhackers who gained access to information on 77 million customers.The company was criticized by U.S. lawmakers after the hacking.

–With assistance from Yuji Nakamura in Tokyo.

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