Cain and abel :- A utility for hackers

Cain & Abel is a password recovery utility that allows easy recovery of various kind of passwords by sniffing the network, cracking encrypted passwords using Dictionary, Brute-Force and Cryptanalysis attacks, recording VoIP conversations, decoding scrambled passwords.It contains a lot of new features like APR (Arp Poison Routing) which enables sniffing on switched LANs and Man-in-the-Middle attacks.

Ok now without talking too much , i will recommend you to watch this video ,that what an hacker can do while you are sitting in a restaurant accessing  wi-fi , wihtout noticing that is happening with you

I hope you get an idea what is happening here  .If still have some query then feel free to ask