They claim end-to-end encryption, which means they don't store it unencrypted.
From a wired article about it:
"Textsecure has actually already been quietly encrypting Whatsapp messages between Android devices for a week. The new encryption scheme means Whatsapp messages will now travel all the way to the recipients? device before being decrypted, rather than merely being encrypted between the user?s device and Whatsapp?s server."
From a wired article about it:
"Textsecure has actually already been quietly encrypting Whatsapp messages between Android devices for a week. The new encryption scheme means Whatsapp messages will now travel all the way to the recipients? device before being decrypted, rather than merely being encrypted between the user?s device and Whatsapp?s server."