This from Caldera International's Security Advisory:
The /usr/bin/X11/xlock program contains a potential security problem via a buffer overflow. This could be used by an unauthorized user to gain privilege.
OS: UnixWare 7.
Version: 7.1.0, 7.1.1.
Affected files: /usr/bin/X11/xlock.
OS: Open UNIX.
Version: 8.0.0.
Affected files: /usr/bin/X11/xlock.
Location of fixed binaries can be found at: ftp://stage.caldera.com/pub/security/openunix/CSSA-2001-SCO.34/