Er... I'm not sure. Try other clients, such as ABC.
What kind of security block are you getting? Most BT clients will try to setup a "listening port"
so that others can connect to you and download what you already have. I guess that might
be triggering the security thing. But, it may not be Windows but some Anit-Virus or Firewall
software doing that instead... which can perhaps be configured not to do that.