You get arrested. The authorities run a background check. They need to know if you have outstanding warrants or unpaid tickets, if you jumped bail somewhere, if you’re driving a stolen vehicle. To obtain your criminal history, they routinely send your fingerprints to the Federal Bureau of Investigation, which keeps a database of more than a hundred million prints. The F.B.I., under a federal program known as Se Communities, will share your fingerprints with the Department of Homeland Security.