Its not going to be rpi specific but it will be at risk for any standard exploit for
services it hosts. You could pwn it via apache, dns, mail server, etc but again its mostly
app vulnerabilities and no real blame to the product itself.
For protection it shouldn't have any problem running simple iptables (firewall rules),
clamav (on demand virus scanner) if desired or I suppose even snort or other ids/ips
although thatd certainly take away from the limited resources.
Either way it should have all the charm of the ported OS.