Symantec shed a third of its value Friday in the stock's worst day in 17 years.

Shares fell 33 percent percent to close at $19.52. At one point, shares fell as low as $18.85 — levels not seen since June 2016.

The cybersecurity company, which makes Norton anti-virus software, said Thursday it has launched an internal audit in response to concerns from a former employee.

The company did not elaborate, saying only that the investigation was not security-related.

"The investigation is in its early stages and the Company cannot predict the duration or outcome of the investigation," Symantec said in a statement.

A source familiar with the matter told Reuters it was separate from another investigation launched in November into the possible violations of federal securities laws in relation to its executive compensation awards.