The authors of the Flashback trojan that infected up to 650,000 Macs at its peak may have raked in up to US$10,000 a day, according to estimations released by Symantec.
The company based its calculation on an investigation into another click-fraud scheme last August, which found 25,000 compromised computers could generate revenues of up to US$450 a day.
Flashback contained an ad-clicking component that allowed the attacker to generate revenue. Symantec now believes making money from the trojan was the Flashback creator's "end goal".
The trojan effectively "hijacked" advertising clicks that were intended for Google.
Symantec showed an example where an ad click worth 0.8 cents was hijacked by Flashback.
"This ultimately results in lost revenue for Google and untold sums of money for the Flashback gang," the company said.