ICQ Status Checker allows you to see the status of every user, no matter if he is online, not available, invisible or offline.
Temporarily there is no protection against ICQ Status Checker, that means that every invisible contact can be detected, independently which client he is using. Besides, the XStatus (from status manager), the registration date and the login and idle time will be displayed additionally (in case the user is wheter offline nor invisible).
If you use the anonymous mode even a login is not required. However, if you want to login although it would be the best way to do so by a second anonymous number.