This does not seem to be a stupid brute force attack, as there is only one login attempt per user. Could it be that the tool tries to exploit some vulnerability in the sshd, and just tries to look harmless by using 'test' and 'guest' as usernames?
The compromised machine was running an old debian woody installation which had not been upgraded for at least one year, the sshd version string says 'OpenSSH_3.6.1p2 Debian 1:3.6.1p2-10'
_______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html