If your email address have been compromised it will be easy to hack your forum account, because the user can easily input your bitcointalk username on the forum and click on reset password, a code will be send to your mail which the user can easily use to access your forum account.
Hackers can compromise accounts by sending phishing emails, which is one of the lucrative and effective ways for them to lure their victims. They send you links via emails that appear genuine and cannot be distinguished from fraudulent ones, but which actually include harmful software and instruct you to act swiftly in response to the email delivered.
In order for you to have access to your services, they can ask you for any sensitive information regarding your accounts, such as updating your password or updating your account. All of these actions are taken to compile reliable information about your login information. If you see one posing, be on the alert for this red flag.