Email & password found on ID Theft forum

I just got an email from LifeLock telling me that my email and password have been found on an ID theft forum as a result of keylogging/phishing. I have changed my password. I've been using Norton 360 for several years and have always thought that it would prevent this from happening. I run scans regularly to get rid of tracking cookies but I guess that's not adequate. What am I missing?