marklodge, an forwarded port on the router is not bad, as MrByte stated.It is the service using that port that can be exploited. When the game or whatever that uses that port is not running, the enabling the windows firewall will keep it safe. You can use google searches to help also.
[url]http://www.google.com/search?hl=en&safe=off&client=firefox-a&channel=s&rls=org.mozilla%*Aen-US%*Aofficial&hs=*ab&q=bittorrent+port+exploits&btnG=Search[/url]
You may want to research wep cracking and wpa cracking too.