“We believe this is one of the largest cases of its kind in U.S. history,” U.S. Attorney Nick Hanna told a news conference.

The conspiracy included frauds involving business email, romance scams and schemes targeting elderly people.

Victims were targeted in the U.S. and around the world, and some lost hundreds of thousands of dollars.

Fourteen defendants were arrested, mostly in the Los Angeles region. FBI agents could be seen processing suspects in a downtown Los Angeles parking lot.

Six other defendants are believed to be fugitives in the U.S. and the others are abroad, mostly in Nigeria. Authorities said they hope to extradite them.

The investigation began in 2016 with one victim and a single bank account, said Paul Delacourt, assistant director in charge of the FBI’s Los Angeles office.

It was not clear whether these massive arrests are linked to the arrest early in August of Forbes rated billionaire Obinwanne Okeke, for a similar offense. Or whether the men arrested are also linked with an identified Nigerian business email compromise gang known as SilverTerrier. The group, according to investigators is responsible for most of the scams emanating from Nigeria.

Over the last 12 months, the number of actors associated with SilverTerrier has increased to over 400, and during the last four years, this group has been responsible for over 1 million attacks. This has contributed to a 54 percent increase in BEC scams coming out of Nigeria in 2018, compared to 2017, the analysis found.

In 2018 an average of about 28,000 Nigerian BEC attacks were recorded per month, with particularly high spikes in March and April.