Facebook Stored Hundreds of Millions of User Passwords in Plain Text for Years
(Edit: reworded a bit to make it clear I don't think this is acceptable)Sounds a lot like some service was logging the full body of a signup/login request, which then was readable for anyone with access to the logging/tracing infrastructure.Dumb mistake but it's not hard to imagine this happening,  considering that FB probably has a bunch of services involved in the login/signup flow to prevent bots/spam, abuse, etc.Not to imply this is acceptable, especially at a IT company like FB with vast resources and know how. Raw passwords are an especially big screw-up.
There are a lot of failures here, from actually logging something so sensitive over giving access to so many employees to not noticing this for years. (Assuming this was actually log data).BUT if we are honest, anonymizing log data is rarely a priority. Even if it is, leaking sensitive data can happen easily in a lot of different points in the infrastructure. In actual application code, client + server exception tracing (just imagine a deserialization exception which contains part of the input) , web server, load balancer, proxies, service mesh... 
There is a lot of interesting stuff hiding in the logs at pretty much every company.This is a good time to look in the mirror and audit your logging and tracing data. Unless you are in a highly regulated field like finance/healthcare or  there is a strong company-wide culture for security/privacy with regular audits already, I can almost guarantee you will find at least one data point that should not be where it is.Protecting sensitive data needs to be a big consideration for every dev, ops and especially management, which has to allocate enough time for security reviews and audits.