Don't put harmful code in your Minecraft mod

It's a fairly rare occasion when Mojang addresses modder conduct in Minecraft, but it has once more:

@Marc_IRL Is it against the EULA for a mod to have a blacklist that detects certain player names & forces a crash and world save corruption?
— Enzer (@EnzerDeLeo) December 19, 2013

@EnzerDeLeo Yes. Yes it is.
— Marc Watson (@Marc_IRL) December 19, 2013

@Marc_IRL Should I report mod developers who are doing this to Mojang? What is the proper channel for this?
— Enzer (@EnzerDeLeo) December 19, 2013

@EnzerDeLeo Looks like we reverted some of that language when we did a fix recently. The no malicious code part will be in future terms.
— Marc Watson (@Marc_IRL) December 19, 2013

@EnzerDeLeo If they're a minor offender, please point them at the (future) terms. If they're a major offender, let us know.
— Marc Watson (@Marc_IRL) December 19, 2013

@EnzerDeLeo And by major, they've caused a big inconvenience for a ton of people who've downloaded the mod. We can't police -all- issues.
— Marc Watson (@Marc_IRL) December 19, 2013

@Marc_IRL Thank you for your time. Until the EULA updates may I point to your earlier tweet as proof against malicious code for minor cases?
— Enzer (@EnzerDeLeo) December 19, 2013

@EnzerDeLeo Let's wait until it's official. Until then, you can point at this tweet saying that coding that way makes you a douche. :D
— Marc Watson (@Marc_IRL) December 19, 2013

@Marc_IRL Haha, sounds good! Keep the community updated when this change makes it to a revised version of the EULA! :)
— Enzer (@EnzerDeLeo) December 19, 2013

@Marc_IRL @EnzerDeLeo I am talking to said mod developer right now, currently there is a dispute between this modmaker and another.
— SirusKing (@SirusKing) December 19, 2013

@SirusKing @EnzerDeLeo They need to suck it up and deal with it. The community is tired of that kind of crap, and so am I.
— Marc Watson (@Marc_IRL) December 19, 2013

It's not clear how this will affect code which checks for a mod running with other incompatible mods, where the incompatibility is decided by the modder. People have been inconvenienced by a few mods which check for things and refuse to run if they are found. But it's a possibility that Mojang is about to make such code a violation of its license.

For background on this, see Just thought you guys should see this (new chapter in Greg V mDiyo) on subreddit r/feedthebeast.