In an email to staff, Mr Musk said an unnamed employee made unspecified coding changes to its manufacturing operating system and sent sensitive data to unnamed third parties.
The company did not comment and the allegations have not been verified.
The matter will be investigated, Mr Musk said.
"The full extent of his actions are not yet clear, but what he has admitted so far is pretty bad," he said in the email.
"His stated motivation is that he wanted a promotion that he did not receive.
"As you know there are a long list of organisations that want Tesla to die," he added, citing Wall Street short-sellers, oil and gas companies and rival car makers as being among them.
'Extraordinarily unusual'
In a separate email to staff, Mr Musk said there had been a small fire at a Tesla factory on Sunday.
It was quickly extinguished and did not cause any injuries or significant damage, he added.
The factory fire followed a video tweeted by US actress Mary McCormack of a fire in a Tesla car driven by her husband, British TV director Michael Morris, in Los Angeles.
Tesla said the car fire was an "extraordinarily unusual occurrence".
Last week, Mr Musk said 9% of Tesla's workforce would be cut as part of a restructuring of the carmaker, which has not made an annual profit since it was created nearly 15 years ago.
After reporting a record quarterly loss of almost $710m in the first three months of the year, Mr Musk came in for criticism after he vetoed "boring" questions from analysts.
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