is a web based service that allows you to track online/offline status of your yahoo buddies. You can track even those who are not in your messenger list, your yahoo tracker account is in no way connected to your own yahoo id. There is currently no such tool which tells you whether someone is spying on you using this service or not. The service tracks the online/offline activity of Yahoo messenger user in previous 24 hours, and you can track 12 yahoo users with one account. Data updates after every 10 minutes. Yahoo messenger users will be considered as online even if they are invisible to any number of people (not everyone). Being "on sms" and "on mobile" will also be considerd as online.
Check out this cool Yahoo tracking service .. Yahoo Tracker - tracks online offline activity of yahoo messenger buddies | YahooTracker.com