Recently there is this guy who said he can hack any
e-mail address ending with ".com" within 5-10 minutes.
This happened during IRC-chat. So to prove that he can do it. I gave him my non-improtant e-mail address. the password are in alphanumeric. And the worst part is that within 7 minutes he message me privately and reveal my password.
How does he do it and how can I prevent it.

Your's opinion and help are really neeed. TQ.