If you use ICQ, it is very likely that you will get added by someone else. If this happens, Kopete will display a message which contains the UIN of the person who wants to add you to his list.
To get more information about the person click on Info.... A window will open which contains all the information available about the person.
Now you can authorize or block the person. If you authorize, you can chat with him and vice versa, if you block him, he can't talk with you.