The remote host is missing an update to usermin announced via advisory DSA 1177-1. Hendrik Weimer discovered that it is possible for a normal user to disable the login shell of the root account via usermin, a web-based administration tool.
For the stable distribution (sarge) this problem has been fixed in version 1.110-3.1. In the upstream distribution this problem is fixed in version 1.220. We recommend that you upgrade your usermin package. https://secure1.securityspace.com/smysecure/catid.html?in=DSA%201177-1