Hacking the cams and hacking BI are two separate but related topics.
Hacking into cams seems to happen quite frequently and based on the sheer volume of attacks it should be extremely important to not allow incoming connections from the internet to the cameras.
Hacking into BI could be broken down into two subsets 1) hacking into the Windows OS and 2) hacking into the BI software server. For the former, my confidence in Windows security is somewhat high. Maybe I am being naive but I think an updated Windows install should be safe. For the latter, unfortunately I have no idea what web server technology they are using nor how hardened it might be from attacks. BI uses proprietary software and not open source servers so we really can't tell. Opening the Windows/BI machine to the internet should be taken with some caution but seems to be much safer than exposing the cameras themselves. Preferred way to access BI from the internet would be through a VPN and a hardened VPN package.
As far as virus or other protections, I personally don't think many are worth it.