Google was already under an FTC privacy order, and the agency found the search giant had violated those terms by bypassing the privacy settings in Apple's Safari browser.
That allowed Google to track users' browsing habits and deliver targeted advertising.
However the company claims this was not deliberate (the excuse used when its Street View camera cars were found to have collected Wi-Fi data along with the SSIDs that were being harvested for use in a non-GPS location system).
Google also implied that the discrepancy between the statement about tracking published on one of its web pages and the actual state of affairs was caused at least in part by a change made to Safari by Apple.
The company accepted the penalty without admitting guilt. The pre-existing order came about as a response to the way Google's now-defunct Buzz social networking service exposed users' email contacts.
In related news, the Australian Privacy Commissioner has written to Google asking it to erase the Wi-Fi data collected by the Street View project and to provide independent certification that the job had been done.
The data was supposedly erased last year, but the company recently admitted that parts of it still existed.