If you are worried the computer on which you were using Master Password was compromised, the best advice is to change your master password. The effect of this is that all your site passwords will also change. This is to protect you and ensure that anything that was stolen becomes useless to a hacker. You will need to reset your site passwords through the sites' reset account mechanism, likely relying on your email address, so ensure you have access to that and change its password first.
Don't do this before you have ensured your computer is safe and trustworthy again.