The Federal Bureau of Investigation today warned American students abroad to be mindful of other countries trying to recruit them for intelligence purposes.

More than 280,000 American students studied abroad last year, the FBI said, gaining language and cultural skill that “makes these students tempting and vulnerable targets for recruitment by foreign intelligence officers whose long-term goal is to gain access to sensitive or classified U.S. information.”

The bureau stressed the case of Glenn Duffie Shriver, sentenced to four years in federal prison three years ago for taking $70,000 from the Chinese government to apply for U.S. government jobs.

The FBI said students leaving for study abroad should view a video on the case before leaving the country.

“Foreign intelligence officers don’t normally say they work for intelligence services when developing relationships with students—they claim other lines of work,” the agency warned. “Intelligence officers develop initial relationships with students under seemingly innocuous pretexts such as job or internship opportunities, paid paper-writing engagements, language exchanges, and cultural immersion programs.”

“As relationships are developed, the student might be asked to perform a task and provide information—not necessarily sensitive or classified—in exchange for payment or other rewards, but these demands grow over time. Intelligence officers might suggest that students—upon completion of their schooling—apply for U.S. government jobs (particularly for national security-related agencies).”

The FBI specifically warns students to “minimize your contact with people who have questionable government affiliations.”