The remote host is missing an update to icu announced via advisory DSA 1762-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201762-1

It was discovered that icu, the internal components for Unicode, did not properly sanitise invalid encoded data, which could lead to cross- site scripting attacks. For the stable distribution (lenny), this problem has been fixed in version 3.8.1-3+lenny1. For the oldstable distribution (etch), this problem has been fixed in version 3.6-2etch2. For the testing distribution (squeeze) and the unstable distribution (sid), this problem has been fixed in version 4.0.1-1. We recommend that you upgrade your icu packages.