The P90 might fuck you
No game is perfect and Call of Duty: Modern Warfare is certainly no exception. Although the vast majority of gamers enjoy the game, it's not without its flaws. Glitches, bugs, and balance issues have been a problem with Modern Warfare since launch. While Infinity Ward quickly resolved most of these issues, it is inevitable that some of them will go unnoticed. One of them is the P90 bug.
If players use the P90 and use the FFS Ring Sight, they could be giving their opponent the advantage without even knowing it. It turns out that the Ring Sight behaves similarly to the sniper sight when aiming at a person. It gives off a very noticeable glow. It's not by design either. While it makes sense to add this to sniper rifles, using it on other weapons, especially an SMG, is pretty ridiculous.
While this glow in no way renders the Ring Sight useless, it is a major downside. In a game, a few milliseconds can mean the difference between winning a shootout, you'll need all the help you can get. And having a weapon that gives you away isn't helpful.
It's more than likely that Infinity Ward will jump on this bug pretty soon and fix the problem. But in the meantime, it would be good to make sure to use a different weapon. Or at least change the P90's loadout so it doesn't have a Ring Sight.
Call of Duty: Modern Warfare is currently available on PC, PS4, and Xbox One.
Source.