Very odd. You said "in different locations" which I assume means that you have
used different IPs and or wifi and routers.
Being that this occurs on both Macs and Windows is another mystery.
Being it is occurring on 4 different video cards is another mystery.
What's left that 4 computers have in common? Could be malware but it would have to be
browser specific malware or cross platform malware. Are you having any malware symptoms?
If no one else has an answer as to what is causing this, I suggest you start a new topic in the
malware forum. Virus, Trojan, Spyware, and Malware Removal Logs - BleepingComputer.com