hey!
one easy way to hack ur forums and emails is sending u a keylogger. that's pretty easy. u can put one into an image file, then it runs on the background and it can send emails with the logs to the email of the hacker. then u just need to check the logs for the logins and passwords
if u dont have an anti-virus or a spyware detection tool ur just a lamb in the middle of an african savanna
another reason may be the hotmail's changing passwords with the "secret question" wich is not that secret cause if u know where the contact is from u dont even need to know wich is the right question, u just need to guess the answer.
another way maybe be hacking ur forum and if u have an old version that is also very easy, and if u use the same passwords both on the email and forum login... u know what that means.
try to have ur forum version updated, install and anti virus like
avast! 4 and periodically run an
ad-awarescan
that should solve ur problems, and btw dont forget to have a working firewall