under facebook they fixed some security issues that now renders it less risky than a couple of years before. for example, they finally implement ssl pinning. one of their previous 3 problems involved the enabling of ssl export ciphers. they used a weak algorithm involving so called end to end encryption but with the similar key on both ends. codebreakers could easily analyze the garbled content and decipher the key. the other 2 were enablement of null cipher (obviously a problem) and the use of sslv2 which has security holes with mac post-encryption and 40-bit macs. afterall it's a mac-based app.
it's still not 100% secure. but if you're not messaging your bank accounts and pins and passwords to your lover, it's a useful app to circumvent paying roaming charges for talk and text when you travel to a cuntry with operators which have lousy roaming agreements with your home cellular provider. for a few days stay in the crappy cuntry there's no need to get a pirated prepaid sim from an alley nor subscribe to a local cellular service to eliminate hefty roaming charges. but you have to have free wi-fi as data roaming charges will be worse than talk and text (sms) and make you cry.