Like many platforms, Arkham Intelligence allows its users to earn rewards for referring new customers. Users are given a unique link to invite others to sign up, which then credits them for the referral. However, some people have observed that the unique string used to identify the user is simply their email address, base64-encoded. This is a simple way of encoding a piece of text, which is trivially reversed to expose the email address.
A user who noticed the encoding strategy tweeted: "ABSOLUTE LMAO. ALL #ARKHAM REFERRAL LINKS SHARED ON TWITTER IS DOXXING EVERYONE BECAUSE THE EMAIL IS IN THE REFERRAL URL". They then went on to decode some referral links from anonymous crypto personalities, writing "HOW DOES IT FEEL TO GET DOXXED???"
Arkham Intelligence quickly updated its referral program to use an encryption algorithm that can't easily be reversed in this way, and the CEO apologized for what he said was an early version of creating referral links that was never updated.