Our company has its own internal analytics system and, while their approach could technically work to prevent spoofing, there's other, simpler ways. The first is simple deduplication of received events. This will carve out a large portion of invalid requests, particularly if you have thresholds of time for how frequently a received event is considered valid. The second is to calculate the quartiles and outliers. This allows you to remove all but the most sophisticated spoofing and is good practice to remove ill-behaved browsers and filter out things like malware detection tools that duplicate browser requests if they haven't seen the site before. There's many operations you can do to determine the validity of data received, however who knows how much of this is actually done by analytics providers. We've built our own internal analytics system (and expose it to customers) because existing solutions weren't robust enough for our needs. The biggest lesson has been that trying to get higher than about 98% accuracy on delivered events actually lowered the accuracy of events and using calculations on the backend was more reliable, but requires specific knowledge of the type of events.