Seattle, Washington - Amazon said it has blocked over 1,800 North Koreans from joining the company, claiming that Pyongyang sends large numbers of IT workers overseas to earn and launder funds.

In a post on LinkedIn, Amazon's Chief Security Officer Stephen Schmidt said last week that North Korean workers had been "attempting to secure remote IT jobs with companies worldwide, particularly in the US".

He claimed Amazon had seen nearly a one-third rise in applications by North Koreans in the past year.

The North Koreans, Schmidt said, typically use "laptop farms" – computers in the US operated remotely from outside the country.

He warned the problem wasn't specific to Amazon and "is likely happening at scale across the industry".

Tell-tale signs of North Korean workers, according to Schmidt, included wrongly formatted phone numbers and dodgy academic credentials.

In July, a woman in Arizona was sentenced to more than eight years in prison for running a laptop farm helping North Korean IT workers secure remote jobs at more than 300 US companies.

The scheme generated more than $17 million in revenue for her and North Korea, officials said.

Last year, Seoul's intelligence agency warned that North Korean operatives had used LinkedIn to pose as recruiters and approach South Koreans working at defense firms to obtain information on their technologies.

North Korea runs a 6,000-strong cyber unit known as Bureau 121, which operates from several countries, according to a 2020 Pentagon report.

In November, the US announced sanctions on eight individuals accused of being "state-sponsored hackers", whose illicit operations were conducted "to fund the regime's nuclear weapons program" by stealing and laundering money.

The Treasury Department has accused North Korea-affiliated hackers of stealing over $3 billion over the past three years, primarily in cryptocurrency.