WhatsApp, the extremely popular instant messaging service for smartphones that delivers more than ~1billion messages per day has some serious security problems. I will try to give a detailed analysis on some of the issues.
Encryption
Until August 2012, messages sent through the WhatsApp service were not encrypted in any way, everything was sent in plaintext. When using WhatsApp in a public WiFi network, anybody was able to sniff incoming and outgoing messages (including file transfers). The company claims that the latest version of the software will encrypt messages without giving any details on what cryptographic methods they are using (so it is safe to assume they did not do it the right way, using Public-key cryptography) . Update: their encryption is broken
"WhatsApp is broken" - very insecure
