Updated from May 23

Rounding out a profitable week, Microsoft ( MSFT) CEO Steve Ballmer on Friday sold an additional 10.1 million shares of stock in his company, according to a filing with the Securities and Exchange Commission made public today. Combined with sales on Wednesday and Thursday, the recent transaction means Ballmer has sold 49.4 million Microsoft shares (worth at least $1 billion) in recent days.

Ballmer, who still has more than 421 million shares in his account, said he sold the shares as part of an effort to diversify his personal finances.

"Even though this is a personal financial matter, I want to be clear about this to avoid any confusion," Ballmer said in a prepared statement. "I remain excited about the potential for our technology to change people's lives, and I remain as committed to Microsoft as ever."

Ballmer is the company's second-largest management shareholder behind Chairman Bill Gates, who regularly sells large amounts of Microsoft shares. In fact, Gates, who owns more than 1 billion shares of Microsoft stock, sold 16 million shares in April alone, according to the filing with the SEC.

But unlike Gates, Ballmer sells far less frequently. A check of SEC records shows that until last week he had sold no shares this year. Ballmer did, however, make a gift of 3.8 million shares in late January 2002, according to SEC filings.

In any case, the sale doesn't appear to be causing much of a stir on Wall Street. "I don't see any raised eyebrows," said analyst Victor Raisys of Soundview Technology Group. "He owns nearly half a billion shares; it certainly makes sense to diversify," he said. Soundview doesn't have a banking relationship with Microsoft.

Microsoft, which has lagged behind while much of the tech sector rallied this year, gained 61 cents, or 2.5%, to $24.83 in recent trading on Tuesday.