Hashing is a type of cryptographic security method which turns the information in your customer list into randomized code. The process cannot be reversed.

When you upload your customer list in Ads Manager to create a Custom Audience, the information in your list is hashed before it’s sent to Facebook. Facebook uses this hashed information and compares it to our own hashed information. Then, we help build your audience by finding the Facebook profiles that match and create a Custom Audience for you from those matches.

After your Custom Audience is created, the matched and unmatched hashed information is deleted.

Learn more

• About Custom Audiences from Customer Lists
• About Custom Audiences