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 Secure Communities, will share your fingerprints with the Department of Homeland Security. Homeland Security's core job--the reason it was created--is to prevent terrorist attacks on the United States. Your prints might reveal that you're a suspected terrorist. D.H.S. is also charged with border security. Its Immigration and Customs Enforcement arm, ICE, will run your prints through the D.H.S. database--specifically, its U.S. Visitor and Immigrant Status Indicator Technology Program (U.S.-VISIT) and Automated Biometric Identification System (IDENT), which also contain more than a hundred million prints--searching for a match with people wanted for immigration violations. If a match occurs, ICE can issue a "detainer." Now the local authorities, before they release you, may notify ICE, which may elect to transfer you to federal custody in order to begin deportation proceedings.