The company behind Ghostery, a privacy-focused browser and an ad-blocking browser extension, has apologized for a technical error that occurred last Friday when its staff was sending out GDPR-themed emails. The emails were sent to batches of 500 users at the same time, and every user in each batch was able to see the email addresses of the other users. The company said it stopped email sending operations as soon as it realized what it happened, and published on Saturday instructions on how users could delete their Ghostery accounts.
Source: https://www.bleepingcomputer.com/news/technology/ghostery-tries-to-comply-with-gdpr-but-ends-up-violating-gdpr-in-the-process/