chkrootkit is a tool to locally check for signs of a rootkit. It contains:

chkrootkit: shell script that checks system binaries for rootkit modification.
ifpromisc.c: checks if the interface is in promiscuous mode.
chklastlog.c: checks for lastlog deletions.
chkwtmp.c: checks for wtmp deletions.
check_wtmpx.c: checks for wtmpx deletions. (Solaris only)
chkproc.c: checks for signs of LKM trojans.
chkdirs.c: checks for signs of LKM trojans.
strings.c: quick and dirty strings replacement.
chkutmp.c: checks for utmp deletions.