You would think one-way encryption used for password storage is pretty secure except you can create a lookup table with a list of exposed passwords (big list from the rockyou hack) and dictionary words to see if you get a match since everyone uses the same algorithm. Your password probably won't be compromised if it is unique or if the website "salts" it before encryption. With
Ashley Madison, their source code got released and they used the password in a second database field where it could be potentially extracted.
In practical terms - don't reuse passwords for sensitive websites (banking, paypal, email, etc), use long and unique passwords (non-dictionary words, symbols if allowed, upper and lower case, numbers) and use a separate email to register with websites you want to remain anonymous (
ashley madison, perb....). If your email offers 2 factor authentiction (sends text code to phone for confirmation, available on gmail and hotmail), enable it. Email needs to be secure since hackers can change your website login passwords if they control your email.
I got a weird email once suggesting my anonymous email was no longer anonymous. I created a new one, changed any website login associated with it to the new one (important) and then deleted the old one.