Microsoft has been hit with the loss of another key executive.

Rob Short, the company's corporate VP for Windows Core Technology, has resigned, Microsoft confirmed Tuesday.

Short, a 19-year Microsoft veteran, led the team responsible for designing, developing, and testing core components of the Windows operating system -- the latest version of which is Windows Vista.

"Rob made many contributions to Windows," Microsoft said in a statement confirming his departure. The company said Short left in December.

Short had been on sabbatical for the past year following the release of Vista and decided not to return for personal reasons, a Microsoft spokesman said. Short's resignation marks the third departure of a key Microsoft executive this year.

Last week, Microsoft Business Division president Jeff Raikes said he would retire in September, to be replaced by former Juniper Networks chief operating officer Stephen Elop. Also last week, Microsoft said that mergers and acquisitions chief Bruce Jaffe would retire at the end of February.

To boot, Microsoft chairman Bill Gates will give up full-time duties at the company he co-founded come July.

The departures highlight one of Microsoft's biggest challenges as a mature company -- attracting and retaining talent. In its early days, Microsoft could entice recruits with an entrepreneurial environment and stock options that would eventually turn secretaries into millionaires.

In 2008, however, it's hot Web 2.0 startups like Flickr and MySpace that are offering those kinds of perks and financial incentives.

Microsoft also faces some other problems. On Monday, the European Commission said it launched a new antitrust investigation into Microsoft's business practices. The company has already agreed to pay a $1 billion fine to settle past violations.