A US federal court has ordered a $163 million fine against the operators of a "scareware" scheme which tricked computer users into thinking they were infected, and then sold them a "fix," officials said Tuesday.

The Federal Trade Commission said the court imposed the fine on Kristy Ross and two companies, Innovative Marketing and ByteHosting Internet Services, and permanently barred them from selling computer security software.

The FTC said its probe dated back to 2008 when it charged Ross and six other defendants with scamming more than one million consumers into buying software to remove malware supposedly detected by computer scans.

The FTC charged that the operation used elaborate and technologically sophisticated Internet ads which displayed to consumers a "system scan" that detected a host of malicious software.

Consumers who fell for the scheme would pay $40 to $60 to clean off the malware.

Under a 2011 settlement, two other defendants were ordered to give up $8.2 million in ill-gotten gains. Two others previously settled the charges and the FTC obtained default judgments against three other defendants..