The remote host is missing an update as announced via advisory SSA:2004-222-01.
New libpng packages are available for Slackware 8.1, 9.0, 9.1, 10.0, and -current to fix security issues. These issues could cause program crashes, or possibly allow arbitrary code embedded in a malicious PNG image to execute. The PNG library is widely used within the system, so all sites should upgrade to the new libpng package. More details about these issues may be found in the Common Vulnerabilities and Exposures (CVE) database: