I've had to go out of my way to tell several of my friends now that their account is liking spam posts. The worst part is they don't know it's happening, since

I've had to go out of my way to tell several of my friends now that their account is liking spam posts. The worst part is they don't know it's happening, since they don't see posts their account is liking. The posts getting liked are from fan pages with <5 likes, yet the post gets 10,000 likes within minutes. Is there some reason that isn't easily detectable?