Google knew about the collection of MAC addresses, and has never said otherwise or stated that their collection of these addresses was done accidently.
Conor: Google has clearly stepped into the arena of doing something that could be detrimental to the user's privacy
Google's new report on its activities states, “All available MAC addresses are… written to disk for frames transmitted over both encrypted and unencrypted wireless networks.”
Even many experts don't understand that with network encryption enabled, the sender's and recipient's MAC address are in the clear.
Some comments from readers
Collection of the MAC addresses of phones and laptops is especially worrisome
Once you have snooped peoples’ MAC addresses, and put them into a database linking them to a street address, you have dramatically changed the way network identifiers work.
Stealing one part of the WiFi packet is as bad as stealing another.
MAC database operators will know not only the locations of people who opt into their system, but of people who opt out, since people who opt in report the device identities of those who don't.
But breaches of telecommunications laws may be easier to prove in the case of content than of device-identifiers…