Neither RealNetworks nor Microsoft are clients of Envisioneering Group, although both companies subscribe to the market research firm's newsletters.
Microsoft said it was surprised by RealNetworks's legal action, given the intense competition in the digital media marketplace and the plaintiff's own reported growth, massive distribution of its software and more than a 1 million downloads of its RealOne media player a week.
"Thus, this is a case where a leading firm is seeking to use the antitrust laws to protect and increase its marketplace share and to limit the competition it must face," Microsoft said in a statement.
Some analysts agreed that RealNetworks could compete successfully against Microsoft, if it offers consumers a product better than Microsoft's Windows Media Player. RealNetworks's product can be downloaded for free from the company's web site, and easily installed on Windows.
"As long as it's better, than people are going to continue to use it," Martin Reynolds, analyst for market researcher Gartner Inc., said.