The current state of commercial tracking:

Adobe is (re)selling data from another data broker, who tracked protesters in the US ( https://www.buzzfeednews.com/article/carolinehaskins1/protests-tech-company-spying) and claims to profile users of 1.6bn mobile devices globally by secretly harvesting app+location data: https://www.adobe-audience-finder.com/data_partner/mobilewalla/

Adobe, the data broker:
https://twitter.com/WolfieChristl/status/1198739105275875328

Mobilewalla, a smallish data broker, says it has "2+ years of historical persistence data per device", or even 4 years, according to its website.

And mobilewalla claims to be GDPR compliant, which is almost certainly not the case.

This level of naiveté and irresponsibility is breathtaking:

- "So, why did you analyze individual-level data on protestors?"

- "Just out of curiosity, ya know, and because we can."

https://www.buzzfeednews.com/article/carolinehaskins1/protests-tech-company-spying

When mobilewalla isn't tracking BLM protesters, there's a good chance they are compiling lists of personal IDs referring to people who 'use Islamic apps' and 'were observed frequently in mosques' or 'in food markets that have close proximity to mosques': https://cdn2.hubspot.net/hubfs/4309344/MW%20Audience%20Segments_Ramadan%202020.pdf

Several other large companies are also (re)selling mobilewalla data, for example:

- Oracle:
https://www.oracle.com/ca-en/data-cloud/solutions/data-as-a-service/data-providers.html
http://www.oracle.com/us/solutions/cloud/data-directory-2810741.pdf

- Salesforce:
https://konsole.zendesk.com/hc/en-us/articles/217592967-Third-Party-Data-Marketplace

In 2017, mobilewalla claimed to track:

- 34 million mobile devices in France
- 21m in Germany
- 11m in Italy
- 10m in Spain
- 41m in the UK

...according to a mobilewalla presentation from 2017, hosted on the website of German mobile data broker adsquare: https://www.adsquare.com/wp-content/uploads/2017/03/08_AIM_Mobilewalla.pdf

As a service to EU authorities, here's a detailed summary of personal data processed by mobilewalla:
https://cdn2.hubspot.net/hubfs/4309344/Content%20Offers/Mobilewalla%20Data%20Dictionary_Aggregated_FEB2020.pdf

+ I'd recommend German DPAs looking into mobilewalla's partnerships with German firms adsquare and zeotap:
https://www.mobilewalla.com/for-partners/dmps
https://cdn2.hubspot.net/hubfs/4309344/1-Mobilewalla%20Clients%20and%20Data%20Partners-2019-Nov-19.pdf

"The aggregation is done at the device level" and "performed on a unique 'latitude - longitude …' combination" including device IDs.

Btw. I love their weird understanding of 'aggregate' data, which they claim to share with others:
https://cdn2.hubspot.net/hubfs/4309344/Content%20Offers/Mobilewalla%20Data%20Dictionary_Aggregated_FEB2020.pdf
https://www.mobilewalla.com/business-services-privacy-policy

Oh great, voter profiling, too:

"Since 2016, Mobilewalla has had a huge impact on Republican party politics. Our solutions have helped hundreds of candidates, PACs, and advocacy groups effectively target voters ... In 2017, MWPolitical was spun off..." https://www.mwpolitical.com/ 

"we are able to target individuals based off of where they shop, go to church, go to school, where they travel, what sports team they follow, or what rallies they attend"
https://www.mwpolitical.com 

e.g. data on 'evangelical christians' (h/t @jsrailton):

MWPolitical's CEO said to @josephfcox MWPolitical is not legally tied to Mobilewalla.

However, MWPolitical often mentions Mobilewalla. Its CEO is Mobilewalla's former VP of political/advocacy. MWPolitical uses Mobilewalla data and is very closely related. https://www.vice.com/en_us/article/9353qv/mobilewalla-tracked-protesters-targeted-evangelicals-during-2016-election

I came across Mobilewalla years ago, as a mobile data provider listed by major companies such as Oracle, Salesforce and Adobe. But I never found out where they get their data from.

They sometimes mention they obtain data from 75,000 smartphone apps: https://cdn2.hubspot.net/hubfs/883/MW%20DataNextDecade_May_2020-1.pdf

Most likely, they do not gather it themselves, but buy it from other firms.

According to their Adobe profile, they obtain data via spyware embedded in apps and via 'exchange supply signals'. The latter refers to data harvesting from 'real-time bidding' in behavioral advertising.

Twitter's mobile advertising arm MoPub lists Mobilewalla as one of many 'demand partners' who 'bid on ad inventory through the MoPub advertising exchange' and are 'independent controllers of your data'.

So, Mobilewalla could receive bid data from Twitter:
https://www.mopub.com/en/legal/partners