i think, We chat is much better than WhatsApp in this regard. whatsAapp has become a 'must have' icon for all smartphone users, but there are a number of issues dogging it.
some imp points from a surveying report by a canadian agency on whatsApp
1. WhatsApp stores NON USERS' phone numbers too. They say these phone numbers are stored in an "encrypted form", even after they are identified as NON USERS of this service.
2. WhatsApp states that files that are sent using its messaging service are kept in their servers after delivery during a so-called "short period of time". After this time they are finally eliminated according to their "general retention policies".
3. WhatsApp does not copy nor store the messages sent through its messaging system. Nevertheless, if the recipient is not connected, undelivered messages will be kept in WhatsApp servers and may be stored in those servers for up to 30 days. After this period of time, messages are deleted; and from that moment on messages will only be stored in the emitter's and the recipient's devices. Nevertheless, WhatsApp may store the date and time of delivered messages, as well as the mobile phone numbers of the devices involved.
THE FINAL CONCLUSION BY AGENCY WAS -
if you are a WhatsApp user, you should NOT send any files with private information, documents, medical records, etc. Act just as if the information was going to be seen by people you do not know