you cant "hack the pass" of a email account, you can
1) guess the reset password
2) send FUD trojan via email or backdoored weblink infected with java exploit or pdf
3) spam them and maybe they will enter same pass for other websites e.g paypal
4) social engineering, if there a male, make a new yahoo with something like sexxy_carder_babe_lol@yahoo.com lol...then send virus though messenger (actually same as step 2 but yh you get the idea)
Hope that helped a lil, if not message me and ill explain or give more ideas or vendors icq to making FUD keyloggers/ buying exploits
