Software issue of HTC 820

Dear all, it's my first htc phone that model is HTC 820 dual sim, after few month it's not working properly, when I active data connection it's automatically download some 3rd party apps and show some advertisement without my permission. I already format it, but it's not fixed.. When I reset it Some 3rd party app install without my permission, I can't understand this issue. Is it hacked someone ?