Thread:Extension talk:Scribunto/Security concerns/reply

I imagine there's much more qualified people to answer this than me, but note that this isn't the whole of Lua. Some methods have been disabled due to security concerns, see Extension:Scribunto/Lua reference manual for more details. There's also a limit to the amount of memory and parsing time Lua can use during parsing. Whilst this was likely implemented as a way of spotting which modules/templates perform very badly, it hopefully answers your second concern :)