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This is a paid asset, but now you can easily download Time-cheat prevention Free.
Time-cheat prevention v1.6
Time-cheat prevention
Mobile (iOS, Android) native plugin to prevent cheating by changing phone time in settings. Does not require server and internet connection – works completely offline!
Many mobile games use timer mechanics: restoring lives, delivering upgrades, training units, breeding monsters, etc. But it is very easy to cheat just by changing device time. (OK, sometimes you must turn off internet connection first)
Now it is possible to make reliable timers even without server and internet connection. This plugin uses internal low-level API to retrieve time data that is agnostic to local device time changes.
Package contains:
1) iOS native plugin
2) Android native plugin
3) C# wrapper class with method to return current unbiased time
4) Optional script that uses ntp pool when connected to network. This feature requires .NET sockets (Unity Pro on mobile)
5) Sample project (C#). YouTube demo: http://youtu.be/Yys3cqE2ocE