The Securities and Exchange Commission has launched a formal probe into the stock option practices of video game maker Activision Inc.

The Santa Monica company said it was notified of the formal probe earlier this month, according to an amended quarterly earnings report filed with the SEC,. The agency informally began investigating Activision last July.

More than 200 companies, including about half a dozen in the L.A. area, have disclosed possible errors involved in their stock option practices involving the backdating of options to maximize gains for executives. But few have been formally investigated by the SEC, with most conducting their own independent investigations.

The video game company said last month that correcting its options accounting over a 13-year period ending last year would reduce earnings by $67 million before taxes.

Shares of Activision were down 39 cents, or 2 percent, to $19.18 in afternoon trading Thursday on the Nasdaq.