In my experience with this browser, it is very vulnerable to VIRUSES.
Most of them are TROJANS and most of that (at least on my experience) have been thru JAVA exploits.
When I re-installed Windows 7 64bit I simply avoided (a have not installed) anything that would "require" JAVA to run thus eliminating a lot of unnecessary risks.
Still, I got a virus after that and it was another Trojan (and I'm 100% certain) that it was thru this browser. The truth is that sadly there will always be some moron (very intelligent moron) that will be creating some new way to harm others. Staying away of known (even if look friendly) or especially if they look "too friendly" and "helpful" because most times than not, that's precisely how this threats are masked.