The latest Call of Duty: Modern Warfare Remastered update has introduced microtransactions, adding paid options not included in the original release.
Supply drops--random loot drops first introduced in Call of Duty: Advanced Warfare--return, and are purchasable with Call of Duty Points or Depot Credits, which can be bought using real money or earned in-game. Supply drops only contain cosmetic items, like new weapon camos, different reticles, and new character skins. The same items can all be earned by completing in-game challenges, for those who don't want to fork out more cash.
You can also craft the new items using Parts, Modern Warfare Remastered's version of Salvage from Call of Duty: Infinite Warfare.
Lastly, a bunch of new melee weapons can be purchased, like a shovel or hammer. The existence of these melee weapons, as well as the potential for microtransactions, had previously been leaked.
This same update also introduced female fighters and six more maps--read more about them here.