In a landmark decision, the U.S. Supreme Court ruled Friday that police must obtain a search warrant to access an individual's cellphone location information. The 5-4 decision imposes new limits on law enforcement's ability to get at the increasing amount of data that private companies amass in the modern technological age.

Ed McAndrew, Co-Practice Leader of Ballard Spahr's Privacy and Data Security Group and a former federal cybercrime prosecutor, agreed with some of the dissenters' concerns. He noted that cell location information is often gathered in the early stages of an investigation when there isn't enough information for a search warrant. The same is true in terrorism and national security investigations.

"The national security context is only going to be different if we're dealing with foreign nationals," McAndrew said. "If we're dealing with American citizens, the Fourth Amendment principle is going to apply."

Moreover, cellphone data are more reliable than more traditional sources of information, he said. "[Data] are better witnesses than human beings ... who may be biased, may be uncooperative, may have a faulty memory."

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