From government offices, they obtain computer lists of property buyers.

CNN: TRAPPED IN THE BIG SQUEEZE

Recent high profile data breaches, corporate economic espionage cases and government reports detailing the threat posed by foreign economic espionage in cyberspace have generated more focus on the risks posed by cyber incidents and whether corporations are doing enough to protect their computer systems and intellectual property.

FORBES: Disclosing Cyber Security Incidents: The SEC Weighs In

Fortunately, in 2005, the Fourth Circuit Court of Appeals (in Virginia) upheld federal agents' authority to conduct suspicionless border searches of a person, his personal property and his laptop computer.

WSJ: Roy Altman: Judges For Lax Border Security