Take proper steps to secure your ssh.
I manage a number of OS X Servers (10.4.x) - either public-facing or still reachable via ssh, and have not had this problem.
Set ssh to use a non-standard port (this is NOT extra security, it cuts away the bulk of the dumb/bot scans/attacks), secure ssh at the firewall (allow only the IP ranges you truly need to let in - takes some work but specific ISPs use specific blocks of IPs), and only allow connections via ssh shared keys.
For changing the port, see
http://www.macosxhints.com/article.php?story=20050707140439980
Choose carefully for the alt. port of course.
For ssh keypair auth, see
http://www.afp548.com/article.php?story=20040816224717742