This one is huge. If you have one of the affected systems you want to pay close attention:
IBM AIX versions 4.3 and 5.1
Hewlett-Packard's HP-UX
SCO OpenServer 5.0.6 and earlier
SGI IRIX 3.x
Sun Solaris 8 and earlier
http://www.cert.org/advisories/CA-2001-34.html