A blockchain analysis firm says hackers with suspected links to North Korea stole 1.65 billion dollars' worth of cryptocurrency in 2022.

Chainalysis says that's a four-fold increase on the previous year and the highest in seven years.

The company says there were many cases in which large sums of money were stolen from online game programs.

Some experts say North Korea could be using the proceeds from cyberattacks for nuclear and missile development.

The Japanese government has issued a warning to domestic cryptocurrency businesses about Lazarus Group, a firm believed to be affiliated with North Korean authorities.

Erin Plante, the vice president of investigations at Chainalysis, says crypto theft is a grave security threat for many countries.

She says it is important to prevent the conversion of stolen crypto into cash. She is calling for cooperation between the public and private sectors.