I sympathise Viks I know it can be a nasty problem to deal with and can hurt your forum.
You can alter the template in the admin cp and delete the options for IM ids in a members profile or you can have your settings so that profiles are not available for viewing and the IM id options dont appear at the top of members posts.
I realise that both of these options are drastic but you can always put them back at a later date once things calm down. You will also find your members will suport you if you let them know what you are doing and why and that it isnt a permanent move.
Karen
ps if you would like help from me or other members why not post here
https://vborg.vbsupport.ru/forumdisplay.php?f=97