SAN FRANCISCO, May 10 (Reuters) - The U.S. FBI is

working towards charging hackers from the aggressive Scattered

Spider criminal gang who are largely based in the U.S. and

western countries and have breached dozens of American

organisations, a senior official said.

The young hackers grabbed headlines last year when they

broke into the systems of casino-operators MGM Resorts

International ( MGM ) and Caesars Entertainment ( CZR ), locking

up the companies' systems and demanding hefty ransom payments.

From health and telecom companies to financial services, they

have hacked a range of organisations over two years, piling

pressure on law enforcement agencies to thwart them.

"We are working towards charging individuals where we can

with criminal conduct, in this case, largely around the Computer

Fraud and Abuse Act," Brett Leatherman, the FBI's cyber deputy

assistant director, told Reuters in an interview.

The group was a rare alliance of hackers in Western

countries with veteran cybercriminals from eastern Europe, he

said on the sidelines of the RSA Conference in San Francisco

Wednesday.

"Often we don't see that mingling of geographical hackers

working together outside the confines of like hacktivism, for

example," he said.

Security researchers have tracked Scattered Spider since at

least 2022 and say the group is far more aggressive than other

cybercrime gangs - skilled especially at hijacking the

identities of IT helpdesk staff to penetrate into company

networks. Caesars paid around $15 million to free its systems

from the hackers.

In chats with its victims the group has sometimes threatened

physical violence, alarming some researchers.

There appeared to be a dip in the gang's activities in

January, but they are going "pretty heavy right now," said

Charles Carmakal, chief technology officer at Google's Mandiant

security arm that has worked with several victims.

The gang has targeted over 100 organisations in two years,

gaining some level of access into all of them, and was

successfully phishing people on a regular basis, he said.

Given the intensity of their attacks, some experts have

criticised the lack of arrests, especially since they are based

in Western countries.

Leatherman said private security firms were helping the FBI

gather evidence.

"This is an incredibly important group for us to continue to

look at disruption opportunities for," he said.

"We have a certain burden of proof we have to meet to

conduct law enforcement operations. And we are heading in that

direction as quickly as we can," he said.

There is one known arrest. In January the FBI charged

19-year-old Noah Urban from Florida for wire fraud, who

Leatherman said was with Scattered Spider.

More arrests may be coming. Some of the gang's members are

juveniles, but the FBI could use state and local laws to bring

them to justice, said Leatherman.

"That's historically very, very effective," he said.