The Justice Dept. has charged seven Iranian nationals with computer hacking offences against US banks and a dam in New York.
A grand jury indicted the seven alleged cyberattackers, who had links to the Iranian government, for an "extensive campaign" which lasted just shy of six months.
During their campaign, they are said to have carried out numerous distributed denial-of-service (DDoS) attacks, with one of the attackers separately gaining unauthorized access to a dam's industrial automation control (SCADA) system.
The seven men are accused of disabling bank websites, preventing customers from gaining access to their online accounts, and costing the companies "tens of millions of dollars in remediation costs" in fending off the attacks in various incidents spanning 2011 to 2013.
Court papers say Bank of America, Capital One, ING, PNC Banks, and the New York Stock Exchange were targets.
One of the men charged, Hamid Firoozi, was indicted on a separate count of hacking into a system the Bowman Dam in New York, which according to the Justice Dept. would normally have permitted him to remotely operate and manipulate the dam's sluice gate.
Luckily, the sluice gate had previously been manually disconnected for maintenance at the time of the attack.
The indictment -- an accusation rather than proof of guilt -- was unsealed Thursday at a press conference in Washington DC.
FBI Director James Comey warned that though the cyberattacks were out of reach as they remain in Iran, the agency will "never say never" to seeking their prosecution in the US.
"In unsealing this indictment, the Department of Justice is sending a powerful message: that we will not allow any individual, group, or nation to sabotage American financial institutions or undermine the integrity of fair competition in the operation of the free market," said US Attorney General Loretta Lynch in prepared remarks.
The seven attacks face up to 10 years in prison for computer hacking charges, while Firoozi faces an additional five years for his attack against the dam.