From a nondescript seventh-floor office at 135 Bonham Strand near Hong Kong’s financial district, at least four companies are operating with a shadowy mission: facilitating the illicit trade of Western technology to Russia.

Shell companies at that address have acquired millions of restricted chips and sensors for military technology companies in Russia, many of which have been placed under sanctions by the U.S. government, according to an examination by The New York Times.

The companies have names like Olax Finance and Rikkon Holding. Their office, with a faded 704 on the door, appears unoccupied. No one answered during a visit last month. An ad for air-conditioning hung in the crack of the door.