WhatsApp handles more messages than Apple's iMessage does
bgr.com
bgr.com
i read about it on slashdot, and told my sister, who uses it all the time. her response was "oh, should i care?". sigh
I mean, to put this in perspective: my physical mailbox is secured by a pretty crummy key; it is sufficiently crummy that, early on when I didn't know which mailbox was mine, I found another mailbox near mine shares the same key.
However, if I really wanted to get mail out of the mailboxes, it would not only be trivial to pick any of these old and simple locks, but I bet I could get in to the back with a pair of pliers and put it back together without anyone noticing.
Yet, I don't particularly care: I don't have any of my bank/credit statements go to my apartment, and that's good enough for me, with regards to the security of my mail. If someone really wants to steal it from me, they could... but seriously: "should I care?".
Moreover, it's digital, so most people don't really understand how any of it works and there is a much larger attack vector than the inherent physical locality required by stealing someone's mail.
What's app should be secure.
In practice, WhatsApp is actually much more secure than most of the things that people trust with their privacy, and this is certainly true for the people against whom most people are specifically attempting to protect their private things from being taken by.
As an example: let's say that an ex-girlfriend of mine decided to stalk me. She can either 1) use a pair of pliers and steal my physical mail, 2) guess a poorly-chosen four-digit PIN number and access my voicemail, or 3) guess my 14-digit IMEI (Android; alternatively, 160-bit UDID on iPhone) and access my WhatsApp account.
In actuality, then, WhatsApp is one of the most secure things I might currently be using to protect my privacy from these kinds of other users. I can easily see someone saying "so, should I care?" about this particular vulnerability.
Of course, for someone else, that might not be the case: if you use WhatsApp for something much more sensitive than I might, or you are attempting to protect yourself from a much more sophisticated attacker than most people are (example: most people really and honestly don't care that a large faceless corporation knows you hated your sister's cheesecake), then you probably do (and certainly should) care.
[1] They wouldn't even have to write iMessage apps for those devices--just allow, say, WhatsApp, to use the iMessage protocol.