Hence my original recommendation that you use something like Smoothwalls built in VPN. Smoothwall also has a virus scanner built in, not the best but it should help to catch some of that stuff.
On another note, it is one thing when you use a VPN for your own access out in the wild, you know what the security of the end points of the connections are. When you start to connect to other networks which you have no control over then you are as good as wide open to every hacker on the internet. Also keep in mind that you may have your portal to the internet locked down and secured but on the other side if they get through the security there, they are in you from the backside! In more ways than one maybe.
I would be willing to bet good money that you will never see a VPN server in NASLite.
Mike