to secure yourself
A. keep your windows updated
B. get a good firewall
C. get a good antivirus
a forwarded port on your router is not a risk by itself.
a trojan could take advantage of it, yes, but
1. you should make your best to not run any trojan
2. a good firewall would warn you of it, even if the router is "open"
3. with no UPnP enabled, a trojan would spend a lot of time/resources to realize IF AND WHICH port is open
so, respect points A,B,C and don't worry