Why is factory reset unable to remove malware?

[naimshaikh]

By mistake i have installed some battery booster apps on my android 4.2.2 and got infected, i have uninstalled those apps and
performed factory reset but to my surprise virus is back. threats: 4
1 : com.vwydya.snslxcjby (trojan)
2: com.nb.superuser (trojan)
3: com.nb.superuser (potentially unwanted app)
4: com.clrrlixw.hmotzhoh (potentially unwanted app)

I have disabled auto reset before factory reset but failed.

my device seems rooted by malware (anti virus says so while cleaning threats)

Please help

 

[Rukbat]

A factory reset resets the phone by removing anything you've changed - it doesn't change any system apps. If the virus installs as a system app, a reset won't touch it. Reflashing the ROM will get rid of anything, though. (The download mode is like a separate operating system - it shouldn't have gotten infected - and that's how you reflash the ROM.)