A minor point…I think you mean to say “SSH” not “SSL”.
I wouldn’t worry too much about this. There are other ways that your user name can be discovered (eg, in email). That said, DH might be fixing this, because I find that I can’t list other user names when I use SSH. You can mention this to Support and see what they say.
A brute force attack would involve trying different passwords in the hopes of finding the right one. You can defeat this by choosing a password that it unlikely to be guessed. (You can even have the DH admin panel generate a password at random.)
You can couple this with public key authentication to make it easy for you to log in from your Mac (and only your Mac) without having to memorize the obscure password. Here’s one set of instructions to get you started:
Look for the section “Passwordless logins with SSH”. In this case, your Mac would be the client, and the DH machine the server. There’s also an application to help set this up http://www.gideonsoftworks.com/sshhelper.html, but I haven’t used it myself.