Hrrm, now, I'm not sure how or why noone would have done this long ago, but in terms of ICQ, to prevent spam:
1) Turn ON/enable 'Do not accept WWPager Messages'
2) Turn ON/enable 'Do not accept EmailExpress messages'
3) Turn ON/enable 'My authorization is required before users can add me to their contact lists'
4) Turn ON/enable 'Accept messages only from users on my Contact List'
5) Turn ON/enable 'Do not accept Multi-Recipient Messages from All Users'
With these settings, the only spam I get is forwards from users on my contact list that sent it to me only. I can deal with those. The above settings work for me, you'll notice when you go into ICQ's settings to change them that there are options for less restrictive/anal settings. Understand that the easier you make it for people to send you messages, the easier it is for spam to come through. Just a word of warning.