stop file transfers for msn messenger

[brorsans]

Hi

I have people that wants to chat on MSN Messenger v7.5. Thats fine with me but they keep sending or recieving files which i dont like.

Ive searched both this forum and the internet and found that i should block ports 6891-6900, which i did, dont work.
Whats should i do next.

I use SOCKS Proxy server for the MSN Messenger (192.168.0.5)