Hi,
i don't know, if YOUR site is totally unprotected. But this should be no mambo-specific problem. Of course, mambo-sites have been hacked in the last week, but there are security-patches and the mentioned doc.
As i said before: the security of your system / network architecture can not be checked by talking about it in a forum. If you are not sure, if there are security problems, contact a technician. Not only for the security of YOUR site/data/... . There are several nice tricks, where people can hijack your server and use it for spamming or (even worse) as FTP-server for porn or protected material.
BTW, why do you use an own server? Why not host at a professional company. That's not too expensive. Several threads here discuss hosters.
Greetings, Zork
(P.S.: we talk again after "you" met sweden

)