Zynga is the maker of some ‘social games’ that are played by millions of people (e.g.: FarmVille).
You generally log in on a site (typically Facebook) and connect to Zynga by playing a game.
1. How to delete your (hidden!) account at Zynga? Send a mail to to email@example.com. Place “Delete My Account” in the subject line and include your first name, last name, e-mail address and user ID number for the SNS from which you access our games (if applicable) in the body of the e-mail.
2. How to delete a game? See http://www.zynga.com/privacy/removal.php
(From their FAQ)