“It’s inevitable: if your computer is Internet-connected you
will have people coming a-knockin’. Fortunately Linux users are
more savvy than to think any keep-alive ping or other piece of
Internet flotsam is a hack attempt. Even so, it’s simply a matter
of time before your router’s lights flash heavily and
/var/log/auth.log (/var/log/secure on Red Hat) fills with chilling
messages like these:
$ tail /var/log/auth.log
Aug 1 20:23:41 zugzug sshd[15577]: (pam_unix) authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=61.218.125.178
Aug 1 20:23:44 zugzug sshd[15577]: Failed password for invalid user edward from 210.48.230.5 port 43812 ssh2