TikTok

For TikTok, 2019 closed with ominous news: Both the US Army and Navy banned it on the grounds of security concerns. But that doesn't change the fact that 2019 was a slam dunk year for the Chinese social media app. With over 700 million downloads around the world, according to data firm Sensor Tower, it was the second most downloaded app of the year. It beat both Facebook (just under 700 million downloads) and Facebook Messenger (just over 700 million downloads).

The worldwide No. 1 app was WhatsApp, with over 850 million downloads, likely buoyed by its popularity in India. (TikTok too was helped by the ultra-populated country, as Sensor Tower said 45% of its first-time downloaders were in India.) WhatsApp's growth in the fourth quarter of 2020 was up 39% over the previous quarter, Sensor Tower noted.

Sensor Tower

TikTok is a social media app in which users, mostly teens and young adults, post short videos of up to 15 seconds long, often synced with music. It uses an algorithm to learn what you like -- by assessing what types of videos you watch and how long you watch them for -- to cater content to you on its main feed. The app has been downloaded over 1.5 billion times and is owned by Chinese firm ByteDance, currently the most valuable startup in the world.

The app has come under increasing scrutiny in recent months. Not only is the US government suspicious of Huawei and its potential to harm national security, but ByteDance and TikTok have been accused of being threats to user privacy, security and free speech. A proposed class-action lawsuit filed in California claims the app has been illegally and secretly harvesting personally identifiable user data and sending it to China, for instance.

These suspicions haven't led to a blacklisting, as in the case of Huawei. But the US Army has banned TikTok from use on government phones following guidance from the Pentagon. Earlier, the US Navy banned the Chinese app from government-issued mobile devices because of cybersecurity concerns.