CNet reports that administrators of email systems based on Microsoft's Exchange might have spammers using their servers to send unsolicited bulk email. Aaron Greenspan, a Harvard University junior and president of consulting company Think Computer, published a white paper Thursday detailing the problem, discovered <A HREF="http://news.com.com/2100-7355_3-5107904.html">when a client's server was found to be sending spam</A>. Greenspan's research concluded that Exchange 5.5 and 2000 can be used by spammers to send anonymous email. He says even though software Microsoft provides on its site certifies that the server is secure, it's not.