Activision has sent cease-and-desist letters to two makers of popular fan clients for legacy Call of Duty titles in recent weeks. The move cuts off access to the many gameplay and quality-of-life improvements brought by these clients and stops what fans say is the only safe way to play these older games without the threat of damaging hacking by opponents.

The first victim of Activision’s recent efforts was SM2, a major Modern Warfare 2 modding project whose development started over two years ago. Since then, the modding group has been working on updating that seminal 2009 release with new weapons, in-game perks, a redesigned UI, new streak and progression systems, and even a recent move to a more modern game engine.

Those efforts stopped last week, though, before the mod could even release its first version. The SM2 Twitter account reported that “a team member received a Cease & Desist letter on behalf of Activision Publishing in relation to the SM2 project. We are complying with this order and shutting down all operations permanently.”