Regarding firewall option in yahoo messanger

Hi all,

Today I have opened the yahoo messanger and go through the connection option. there I found four more option

1) No proxies 2) firewall with no proxies 3) Use proxies 4) No proxies is found

Can any body tell me what is the significance of this options and what is the concepts behind these option?

What effect these option do on audio confrence? I also have gone through the third one firewall with no proxies options.

What is the use of these proxies in yahoo messanger? Can any body help me to give the answer of these queries?

Thanx in advance

Regards, Ravi