Whatsapp use to use IMEI reversed and md5 hashed as its password on Android (username was the users telephone number) - on iPhone they used a MAC address. I brought it up as a security concern back in 2012.
It would not surprise me if some apps still use IMEI (or MAC address) for similar purposes…
It would not surprise me if some apps still use IMEI (or MAC address) for similar purposes…