WhatsApp has amassed two billion users, up from 1.5 billion by the end of 2017, the company announced on Wednesday. The mobile messaging app was founded in 2009 and acquired by Facebook (FB) in 2014. The deal was valued at $19 billion, the largest acquisition by the social media giant to date. Despite its size, WhatsApp’s growth remains robust: It has gained 500 million new customers over the past two years. WhatsApp touts its end-to-end encryption technology, which ensures that all contents in chats are secured by default. Not even WhatsApp can read messages or listen to calls that take place among the participants of conversations, according to WhatsApp’s blog posts. But the encryption technology has drawn backlash across the world for security reasons. In India, where WhatsApp has more users than any domestic messaging apps, the government has called for regulations that give it access to encrypted data. In Australia and the United Kingdom, similar laws are also in discussion. In October, US Attorney General William Barr asked Facebook to delay its plans to encrypt messages on its platform, citing that information relating to terrorism and sex trafficking can be spread across encrypted messaging apps. WhatsApp strongly defends its encryption technology. “We will not compromise on security because that would make people less safe,” according to WhatsApp’s announcement on Wednesday. “For even more protection, we work with top security experts, employ industry leading technology to stop misuse as well as provide controls and ways to report issues — without sacrificing privacy.”