On October 17, 2018, the French data protection authority (the “CNIL”) published a press release detailing the rules applicable to devices that compile aggregated and anonymous statistics from personal data—for example, mobile phone identifiers (i.e., media access control or “MAC” address) —for purposes such as measuring advertising audience in a given space and analyzing flow in shopping malls and other public areas. Read the press release (in French).

The CNIL observed that more and more companies use such devices. In shopping malls, these devices can (1) compile traffic statistics and determine how many individuals have visited a shopping mall over a limited time range; (2) model the routes that individuals take through the shopping mall; and/or (3) calculate the rate of repeating visitors. In public areas, they can (1) determine how many individuals walked past an audience measuring device (e.g., an advertising panel); (2) determine the routes taken by these individuals from one advertising panel to another; (3) estimate the amount of time individuals stand in line; (4) assess the number of vehicles driving on a road, etc.

Against that background, the CNIL identified the three following scenarios:

Scenario 1 – When data is anonymized at short notice (i.e., within minutes of collecting the data)

The CNIL defines anonymization as a specific data processing operation which renders individuals no longer identifiable. (Such processing must comply with various criteria set forth in Opinion 05/2014 of the former Article 29 Working Party on anonymization techniques. According to the CNIL, this includes ensuring a high collision rate between several individuals—for instance, in the context of MAC-based audience measurement devices, the processing must allow multiple MAC addresses to match the result of single-identifier processing.)

In this scenario, anonymization must be performed promptly, i.e., within minutes of collecting the data. In the CNIL’s view, this reduces the risk that an individual would be able to access identifying data. To that end, CNIL recommends anonymizing the data within 5 minutes. After that period, no identifying data should be retained.

The CNIL noted that data controllers may rely on their legitimate interest as a legal basis for the processing under the EU General Data Protection Regulation (“GDPR”). The CNIL recommended, however, that data controllers provide notice to individuals, using a layered approach in accordance with the guidelines of the former Article 29 Working Party on transparency under the GDPR. The CNIL provided an example of a notice that would generally satisfy the first layer of a layered privacy notice, though emphasized that notice should be tailored to the processing—particularly with respect to the individuals’ data protection rights. Since the data is anonymized, individuals cannot exercise their rights of access to and rectification of their personal data, and restriction to the processing of their data. Therefore, the notice does not have to mention these rights. However, individuals must be able to object to the collection of their data, and the notice should refer to that right of (prior) objection.

Scenario 2 – When data is immediately pseudonymized and then anonymized or deleted within 24 hours

In this second scenario, data controllers may rely on their legitimate interest as a legal basis for the processing provided that they:

  • Provide prior notice to individuals;
  • Implement mechanisms to allow individuals to object to the collection of their data (i.e., prior objection to the processing). These mechanisms should be accessible, functional, easy to use and realistic;
  • Set up procedures to allow individuals to exercise their rights of access, rectification and objection after data has been collected; and
  • Implement appropriate technical measures to protect the data, including a reliable pseudonymization process of MAC addresses (with the deletion of the raw data and the use of a salt or key). The pseudonymized data must be anonymized or deleted at the end of the day.

Further, the CNIL recommended using multiple modalities to provide notice to individuals, such as posting a privacy notice at entry and exit points of the shopping mall, on Wi-Fi access points, on every advertising device (e.g., on every advertising panel when the processing is carried out on the street), on the website of the shopping mall, or through a specific marketing campaign.

With respect to the individuals’ data protection rights, the CNIL made it clear that individuals who pass audience measuring devices must be able to object to the collection and further processing of their personal data. Companies wishing to install such a device must implement technical solutions that allow individuals to easily exercise this right of objection both a priori and a posteriori: these solutions must not only allow individuals to obtain the deletion of the data already collected (i.e., to exercise their right of objection a posteriori) but also prevent any further collection of their personal data (prior objection). In the CNIL’s view, the right of objection can be exercised using one of the following means:

  • Through a dedicated website or app on which individuals enter their MAC address to object to the processing. (The data controller is responsible for explaining to individuals how to obtain their MAC address so that they can effectively object to the processing of their data.) If an individual exercises his/her right of objection via this site or app, the data controller must delete all the data already collected and must no longer collect any data associated with that MAC address; or
  • Through a dedicated Wi-Fi network that allows the automatic collection of the devices’ MAC address for the purposes of objecting to the processing. If an individual exercises his/her right of objection via this network, the data controller must delete all the data that has been already pseudonymized and must not further collect the MAC address. The CNIL recommended using a clear and explicit name for that network such as “wifi_tracking_optout”.

According to the CNIL, data controllers should not recommend that individuals turn off the Wi-Fi feature of their phone to avoid being tracked. Such a recommendation is inadequate for purposes of enabling individuals to exercise of their right of objection.

Scenario 3 – All other cases

In the CNIL’s view, if the device implemented by the data controller does not strictly comply with the conditions listed in the two previous scenarios, the processing may only be implemented with the individuals’ consent. The CNIL stated that individuals must be able to withdraw consent, and that withdrawing consent should be as simple as granting consent. Individuals should also be able to exercise all the other GDPR data protection rights. In terms of notice, the CNIL recommended providing notice using multiple modalities (as in the second scenario).

Data Protection Impact Assessment and CNIL’s Authorization

The CNIL also reported that, in all the above scenarios, the processing will require a data protection impact assessment to be carried out prior to the implementation of the audience/traffic measuring devices, in so far as such devices assist in the systematic monitoring of individuals through an innovative technical solution.

Additionally, the CNIL’s prior authorization may be required in certain cases.