A senior U.S. official said North Korea has thousands of highly skilled IT workers around the world, some of whom were previously employed at U.S. firms under fake identities.

Jung Pak, U.S. deputy assistant secretary for multilateral affairs and deputy special representative for North Korea, made the remarks on Wednesday during a related symposium in San Francisco jointly held by the U.S. and South Korea.

Pak said that a number of the IT workers from the North were hired by U.S. companies, some of which were hacked and suffered long-term damage.

The U.S. official said that the workforce is located everywhere, from Asia and the Middle East to Africa, adding that these workers may make much more money than the average North Korean, but 90 percent of their income is collected by the regime.

Citing UN data, Pak said that the contribution of the IT workforce to the North's ballistic missile program is estimated at over 500 million dollars a year.