Mobile operating systems like Symbian and modern Java implementations require apps to be "signed" with a digital certificate. This ensures the app comes from a trusted source and hasn't been tampered with.

Contrary to popular belief, WhatsApp did not start as an Android or iOS app. It was founded in 2009 by Brian Acton and Jan Koum, former Yahoo employees.

When WhatsApp was first launched in 2009 by Brian Acton and Jan Koum, smartphones were not yet ubiquitous. The first version of WhatsApp was developed exclusively for the . However, to capture the massive market of feature phones, WhatsApp Holdings (before the Facebook acquisition) released a Java ME version of the app around 2011-2012.

A: No official version exists. Any link claiming otherwise is fake or malicious.