A woman working as a real estate agent in California has been arrested on charges of spying for China, accused of tracking the son of Taiwan's president — a sign of how far Beijing's surveillance reaches inside the United States.

• Wanying "Heather" Zhang was arrested at Los Angeles airport as she prepared to board a flight to Shanghai, charged with acting as an unregistered agent of a foreign government.
• Prosecutors say she and another person flew to Seattle in September, rented a car, and photographed the suburban home of Lai Ching-te's eldest son, an engineer who works for Philips.
• Messages pulled from her iCloud account allegedly show her texting a Chinese government contact that she had spotted the target and was filming, then sending two license plate numbers.
• The FBI says she was recruited in China in June through a classmate from a Beijing university with close ties to China's state security ministry, and accepted the assignment at a private meeting.
• The case fits a pattern: a secret Chinese police station in Manhattan, a conviction for infiltrating a New York dissident group, and a former California mayor who pleaded guilty this year to working for Beijing.

Outlook: Expect more U.S. prosecutions of this kind, and sharper warnings to the families of Taiwanese officials living abroad as tensions over Taiwan grow.