At a previous job we tracked unique visitors to prevent ad fraud. You'd find not only individual IPs with thousands of users behind them, but also larger popula

At a previous job we tracked unique visitors to prevent ad fraud. You'd find not only individual IPs with thousands of users behind them, but also larger populations of users numbering in the tens of thousands behind a small block of 8-16 IPs. The craziest was a large multinational corporation that (I guess for security?) changed their egress IP daily. The first three octets remained the same and the fourth was equal to the day of the month UTC. Really screws things up when you use a 14 day rolling window of previous traffic for comparisons.