The remote host is missing an update to asterisk announced via advisory DSA 1952-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201952-1

Several vulnerabilities have been discovered in asterisk, an Open Source PBX and telephony toolkit. The Common Vulnerabilities and Exposures project identifies the following problems: CVE-2009-0041 It is possible to determine valid login names via probing, due to the IAX2 response from asterisk (AST-2009-001). CVE-2008-3903 It is possible to determine a valid SIP username, when Digest authentication and authalwaysreject are enabled (AST-2009-003). CVE-2009-3727 It is possible to determine a valid SIP username via multiple crafted REGISTER messages (AST-2009-008). CVE-2008-7220 CVE-2007-2383 It was discovered that asterisk contains an obsolete copy of the Prototype JavaScript framework, which is vulnerable to several security issues. This copy is unused and now removed from asterisk (AST-2009-009). CVE-2009-4055 It was discovered that it is possible to perform a denial of service attack via RTP comfort noise payload with a long data length (AST-2009-010). For the stable distribution (lenny), these problems have been fixed in version 1:1.4.21.2~dfsg-3+lenny1. The security support for asterisk in the oldstable distribution (etch) has been discontinued before the end of the regular Etch security maintenance life cycle. You are strongly encouraged to upgrade to stable. For the testing distribution (squeeze) and the unstable distribution (sid), these problems have been fixed in version 1:1.6.2.0~rc7-1. We recommend that you upgrade your asterisk packages.