How do I prevent unauthorized ssh login attempts?

[Andreas Widerøe Andersen]

I'm getting a lot of unauthorized ssh login attempts. I have a pretty basic
FreeBSD 6.2 setup. I have compiled my own kernel. Here's what I get from my
daily security run output:

myserver.domain.com login failures:
Apr 25 20:00:19 myserver sshd[57810]: Invalid user staff from 65.171.74.26
Apr 25 20:00:22 myserver sshd[57812]: Invalid user sales from 65.171.74.26
Apr 25 20:00:24 myserver sshd[57814]: Invalid user recruit from 65.171.74.26
Apr 25 20:00:26 myserver sshd[57816]: Invalid user alias from 65.171.74.26
Apr 25 20:00:28 myserver sshd[57818]: Invalid user office from 65.171.74.26
Apr 25 20:00:30 myserver sshd[57820]: Invalid user samba from 65.171.74.26
Apr 25 20:00:32 myserver sshd[57822]: Invalid user tomcat from 65.171.74.26
Apr 25 20:00:34 myserver sshd[57824]: Invalid user webadmin from
65.171.74.26
Apr 25 20:00:36 myserver sshd[57826]: Invalid user spam from 65.171.74.26
Apr 25 20:00:38 myserver sshd[57828]: Invalid user virus from 65.171.74.26
Apr 25 20:00:41 myserver sshd[57830]: Invalid user cyrus from 65.171.74.26
Apr 25 20:00:43 myserver sshd[57832]: Invalid user oracle from 65.171.74.26
Apr 25 20:00:45 myserver sshd[57834]: Invalid user michael from 65.171.74.26
Apr 25 20:00:47 myserver sshd[57836]: Invalid user ftp from 65.171.74.26
Apr 25 20:00:49 myserver sshd[57838]: Invalid user test from 65.171.74.26
Apr 25 20:00:51 myserver sshd[57840]: Invalid user webmaster from
65.171.74.26
Apr 25 20:00:53 myserver sshd[57842]: Invalid user postmaster from
65.171.74.26
Apr 25 20:00:56 myserver sshd[57844]: Invalid user postfix from 65.171.74.26
Apr 25 20:00:57 myserver sshd[57846]: Invalid user postgres from
65.171.74.26
Apr 25 20:00:59 myserver sshd[57848]: Invalid user paul from 65.171.74.26
Apr 25 20:01:04 myserver sshd[57852]: Invalid user guest from 65.171.74.26
Apr 25 20:01:06 myserver sshd[57854]: Invalid user admin from 65.171.74.26
Apr 25 20:01:08 myserver sshd[57856]: Invalid user linux from 65.171.74.26
Apr 25 20:01:11 myserver sshd[57858]: Invalid user user from 65.171.74.26
Apr 25 20:01:13 myserver sshd[57860]: Invalid user david from 65.171.74.26

How can I stop these attempts or block them - or even recognize them? I do
not have IPF installed.

Thanks for your help.

Best regards,
Andreas