The remote host is missing an update to xtrlock announced via advisory DSA 649-1.

https://secure1.securityspace.com/smysecure/catid.html?in=DSA%20649-1

A buffer overflow has been discovered in xtrlock, a minimal X display lock program which can be exploited by a malicious local attacker to crash the lock program and take over the desktop session. For the stable distribution (woody) this problem has been fixed in version 2.0-6woody2. For the unstable distribution (sid) this problem has been fixed in version 2.0-9. We recommend that you upgrade your xtrlock package.