Theres an option in ICQ to only accept messages from contacts. I turned that on, and haven't received any since
I used to get at least 10 a day...drove me NUTS, especially when I was in photoshop, and working with layers, then fucking ICQ pops up on the bottom right lol - which is always pretty annoying, but when it's fucking spam, it just makes it all the more infuriating lol