[moxie]

WhatsApp doesn't use TLS, and their protocol has a fairly long history of criticism.

[josh2600]

http://www.neowin.net/forum/topic/1148702-realized-that-what...

I seem to remember their authentication was a combination of your phone number and the IMEI of your handset, which is woeful security through obscurity at best.

[spyder]

and it seems somebody got so angry about they security that he made this site: http://www.whatsappsucks.com