The phrase "extremely careless" is correct and usable in written English.
It can be used to describe a high degree of negligence or lack of attention to detail in someone's actions or decisions.
Example: "The report was filled with errors, indicating that the author was extremely careless in their research."
Alternatives: "highly negligent" or "very reckless."
Comey then described Clinton as "extremely careless" in handling "very sensitive, highly classified information".
But the FBI determined in July that while Clinton was "extremely careless" it would not recommend charges against her.
Still, he characterized Mrs. Clinton's handling of classified information during her years at the State Department as "extremely careless".
But Comey rebuked Clinton and her aides for the "extremely careless" manner in which the emails were handled.
JAMES B. COMEY: "There is evidence that they were extremely careless in their handling of very sensitive, highly classified information.
However, Comey also announced that Clinton and her team had been "extremely careless" in their handling of classified information.
The US justice department declined to prosecute Clinton over her email practices, though the FBI director, James Comey, called her "extremely careless" in handling classified information.
She was judged to have been "extremely careless" and the issue flared up again in late October when the FBI said it uncovered a new batch of emails.
He called their practices "extremely careless", but said that agents could not find evidence of intentional wrongdoing, obstruction of justice or "vast quantities" of data breached.
"I'm confident whatever they are will not change the conclusion reached in July," she concluded, alluding to Comey's finding of "extremely careless" email practices but no criminal wrongdoing.
In July, Comey had announced that Clinton and her aides were "extremely careless" but that "no reasonable prosecutor" would bring a case against them.
