I agree with Manfred on this one. If it can glow as bright as a torch, it either is operating as a very powerful chemical (non-magic) which would rapidly eat the wood (where else does it get the energy?), or it is magical (and would detect as magic). If magic, where did it come from and why?
The fact that it works on weapons tells me it is magical, or it would have to also convert metal into food for the fungus(and thus power the luminescence :))
So, in summary - if it is natural, then it would need to be toned down and extract energy from both wood and metal. If magic, then some info on it's origins and purpose.
I concur with Manfred - it depends on the logic of the 'language' used. If the spell is a logical process, then yes, an alteration would stand out, but if it properly arcane and barely understood even by its best practitioners, then Trojans and worms should be able to hide in suitably complex spells.