Viber isnt a terrible app, calling it a terrible/bad app would be an insult to other bad apps. viber is the worst app and the worst platform, it is below what is humanly possible.its one of the main reasons i hate the maldivian community as a whole. this can be attributed to its shitty/dark origins (spying tool created by the ISRAELI goverment), although they tried to hide its past or origins some still remains available (https://web.archive.org/web/20131010072724/http://www.moh10ly.com/home/security/viberisaspy), although they claim the app is fully end to end encrypted theres no proof to back it up
privacy on viber is basically non existent, in fact its literally inviting predators and other potential dangerous people to you, Id not be surprised if majority number leaks or similar are through viber