Hello!
- Yes there are security measures, however, no leaderboard system is always safe. Even AAA games get hacked entries in their leaderboards. The only way to keep it 100% clean is to regularly monitor it, verify scores and remove potentially hacked entries.
- Technically, yes. There is no direct way of doing it, but you can message me on Discord (username: @danqzq) and we can figure out a way to synchronize user's progress across different devices.