The remote host is missing an update as announced via advisory SSA:2009-170-01.

https://secure1.securityspace.com/smysecure/catid.html?in=SSA:2009-170-01

New libpng packages are available for Slackware 8.1, 9.0, 9.1, 10.0, 10.1, 10.2, 11.0, 12.0, 12.1, 12.2, and -current to fix a security issue. Jeff Phillips discovered an uninitialized-memory-read bug affecting interlaced images that may have security implications. More details about this issue may be found in the Common Vulnerabilities and Exposures (CVE) database: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-2042