So I never noticed this before, but if you are a big enough publisher Google has a line item for the invalid traffic amount that is taken out of your payment. One account I manage is big account, but in looking back over the last 12 months - the highest amount taken out for invalid traffic was the cost of a large pizza. However, in February this amount was the equivalent of a mortgage payment on a modest home. Quite the increase + it was already a month where earnings before invalid traffic was down 25-30%.
You might want to check the payments section to see this data, but again you will probably only see this line item if you are a earning a pretty decent amount. My other account, much lower earnings has never had a line item for invalid traffic and did not again this month.