Twitter sent out an email to anyone who used ads or provided their billing info to twitter and visited ads.twitter.com or analytics.twitter.com. If you viewed your billing info prior to May 20th, 2020 that info was stored in your devices cache.
Does this affect me? What data was impacted?
So far, Twitter knows of no one impacted, however they have no way to track this. The info was stored on your device, which included “email address, phone number, last four digits of your credit card number (not complete numbers, expiration dates or security codes), and billing address.”
This means if you used a shared computer or left your computer unlocked and unattended, someone could have downloaded your private data from cache. This issue is fixed.