Posted by: kent frese
I assume that by "account holder" you mean me, in this case, and not Siteground.com.
maybe i shouldn't have said that :-\ as almost every hacking scenario is different.
For the record, I have never used siteground so I don't really know how they configure their servers.
That said, many of joomla's default installation settings are high risk... as compatibility and ease of installation is the higher priority. Many directories are set to 777, the joomla cache and configuration file are within the public_html directory, etc (Full list of risks at the joomla.org security FAQ page).
Also, many 3rd party extensions are unsecure and high risk (As the J! 1.0.12 extension install page incessantly nags)
All these issues have nothing to do with the host.