http://thehackernews.com/2014/12/crash-your-friends-whatsapp-remotely_1.html
I read it and found it really interesting...
"Two India based independent security researchers, Indrajeet Bhuyan and Saurav Kar, both 17-year old teenagers demonstrated the WhatsApp Message Handler vulnerability to one of our security analyst.
In a video demonstration, they showed that how a 2000 words (2kb in size) message in special character set (http://pastebin.com/3efiBva4) can crash Whatsapp messenger app."