A young Taiwanese man on a business trip was pulled aside at Shanghai customs and interrogated for six hours over a short job he once had with Amnesty International — a warning sign for anyone from Taiwan traveling to China.

• Three plainclothes officers took him to a back room, made him unlock his phone, and searched his messages and photos.
• They asked about his work, where its money came from, and whether he had touched human rights issues in Hong Kong, Tibet, or Xinjiang; he gave up entry and flew home.
• China appears to hold detailed files on ordinary Taiwanese people, down to old jobs the person themselves had half forgotten.
• Public résumés, social media, and Taiwan's past large data leaks are likely sources of that information.
• Searching one phone also exposes family, friends, and coworkers, spreading the risk far beyond the traveler.

Outlook: Pressure is building on Taiwan's government to collect these cases, trace where the leaked data came from, and issue clear warnings about who is at risk before traveling to China.