How to remove or disable pop-up alert()/confirm() box from build-in Browser from malware? My young niece install low rating free games from Store and she have no any security concern.

Some malicious application open malicious site which ask for money in alert() and confirm() message boxes.

Because of dumb way how official Browser works it is not possible disable or remove infinitely pop-up boxes or close malicious tabs.

How can I close this tabs?

I only think about factory reset but that method too radical.
First step would be to remove those apps as also suggested by @Giant Tree
These kind of apps are invariably bundled with ads. You can install software recommended here Some program is showing ads on my desktop... How can I catch it?. You don't need to install all, any one is enough (I presume your device is NOT rooted, Adaway requires root)


3.That should hopefully solve your issues related to adware. Adware is different than Malware. If some malware has entered your system,it fools the system and lodges itself deep into your device like a system app. Factory reset will NOT help and only way out is to flash stock ROM again. This article would help you identify malware http://securitywatch.pcmag.com/mobile-security/309980-five-signs-your-android-device-is-infected-with-malware