After closing the deal Microsoft will make Sybari's products available under the Microsoft brand, but prices remain unknown.
Stocks of several anti-virus firms, including Symantec and McAfee, dropped after the announcement that Microsoft is going to release commercial anti-virus products.
Symantec shares fell $1.51, or 6.4 percent, to close at $22.09 in Tuesday trading on the Nasdaq Stock Market, while shares in McAfee dropped $2.14, or 8.2 percent, to close at $23.82 on the New York Stock Exchange.More details at Bizreport
Terms of the deal, the latest in a series of security-related purchases by Microsoft, were not disclosed. Sybari is privately held but had been planning an initial public stock offering. The company estimated its market value at up to $186 million in papers filed to with the Securities and Exchange Commission earlier this month.