CHICAGO — A Chinese-born American convicted of stealing trade secrets from Motorola was sentenced today to 4 years in prison in a case that prosecutors hoped would send a message to those who might be tempted to siphon vital information from U.S. companies.

Hanjuan Jin, who worked as a software engineer for Motorola Inc. for nine years, was stopped during a random security search at O’Hare International Airport on Feb. 28, 2007, before she could board a flight to China. Prosecutors say she was carrying $31,000 and hundreds of confidential Motorola documents, many stored on a laptop, four external hard drives, thumb drives and other devices.

U.S. District Judge Ruben Castillo in February found Jin guilty of stealing trade secrets but acquitted her of more serious charges of economic espionage, explaining that the evidence fell short of proving she stole the information on behalf of a foreign government or entity.

Prosecutors alleged that among the secrets she carried were descriptions of a walkie-talkie type feature on Motorola cellphones that prosecutors argued would have benefited the Chinese military.