Use this T_SQL script to anonymize data from ASP.NET's Membership database.
declare @email varchar(255)
set @email = 'email_to_delete@gmail.com'
update aspnet_profile
set PropertyNames = '', PropertyValuesString = ''
where UserId = (
SELECT UserId
FROM aspnet_Membership
where Email = @email
)
update aspnet_Membership
set Email = 'deleted@deleted.com', LoweredEmail = 'deleted@deleted.com', IsApproved = 0, PasswordQuestion = 'deleted', PasswordAnswer = 'deleted', [Password] = 'deleted'
where UserId = (
SELECT UserId
FROM aspnet_Membership
where Email = @email
)