IBM filed a Form 8-K with the SEC yesterday in which IBM stated, "it has received notice of a formal, nonpublic investigation by the Securities and Exchange Commission concerning IBM's disclosures relating to IBM's first-quarter 2005 earnings and expensing of equity compensation." IBM states that it has been cooperating with the SEC since the start of the informal investigation in June of 2005.
The event that triggered the informal investigation was IBM's announcement of earnings last April. That was the first quarter in which the company expensed options. Analysts complained that guidance given to them just days prior to the earnings release caused their estimates to be inaccurate.