This is a bug that showed up in the most recent Magicka patch. The Devs are aware of it, and hoping to have it fixed by Monday, 3/21.
As many of you've seen there's a new patch up tonight, and it's not behaving as it should for some. Some are getting a message that they are running a "modded" version of the game although they haven't touched a single file. Before I get into technical details let me tell you this - the game still should work fine:
- Even if you get the message - you still can play as normal.
- Modding is still fully possible. Arrowhead & Paradox do very much still support modding and think it's great that there are a bunch of cool mods for the game.
- We also want to support the players who want to score big and end up on the leaderboards.
So what we did for this patch was that we put a check in the game that detects if you have any modified files or not. If it detects modified files it'll show you the message, let you keep playing, but won't register any leaderboard scores, achievements or let you play VAC (steams anti cheat functionality) protected games.
So what's the problem? Well our testing looked fine this week. Modded games showed up as modded and unmodded ran just like before. Now we're seeing that the game is erroneously reporting some games as "modded". I myself am getting mixed results (one computer shows normal while the other shows "modded") while both computers are actually unmodded.
We're looking into exactly what went wrong and expect to have a hotfix up by Monday. We're very sorry for this!
But the good news is that no matter the message no game functionality has been affected. You should still be able to cast spells, kill your friends and revive them as usual.
TL;DR: The game is working just fine, but achievements are currently not being tracked, until the next patch. Everything else is as normal.