Microsoft's Silverlight 4, which is an upgrade to the company's rich Internet browser plug-in platform, is set for release on Thursday, according to Microsoft representatives.

Although the subject of a presentation Tuesday at the Visual Studio 2010 launch event in Las Vegas, the technology will not be available until two days afterward. "This is the fourth release of Silverlight that we've had in the last two-and-a-half years," said Scott Guthrie, corporate vice president of the Microsoft developer division, on Tuesday.