The custom value of a unit is an integer stored for every unit. Its default value is 0. It has no use whatsoever without triggers. That would be under the "Integer comparison" category.
Finally finding about some of the bots that are flooding the users online - bytespider apparently is a huge offender here - ignores robots.txt and comes in from a ton of different IPs
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.