i dont think you can 100% say those clicks were fraudulent based on what you're saying about the IPs. IPs change all the time, even for the same user. AOL was famous for switching IPs after every page request. I'm sure there are loads of other IP providers who do the same.
and those host names that you mentioned -- like host.degaa.net -- if you look up degaa on the web they offer website data and tracking stats. i dont know exactly how it works obviously, but if a wesbite is showing your ad and someone clicks on it, i would imagine that the user gets fed through degaa first, so they can log the outbound click. so if one user clicked your ad a few times on that site, its not impossible for him to have 4 slightly different IPs and appear to come from different versions of degaa.net
and ezzi.net, another one that you mentioned, is a webhost. so maybe this degaa user is hosted with them? that would probably explain why the same user can comes through both degaa and ezzi whilst actually coming from a single site.