Most of the online games these days have some sort of loot box or crate system that are designed for players to unlock in-game items and character cosmetics. Some great examples are Overwatch and League of Legends where they have loot boxes and hextech chest for players to earn while playing the game. Even the newly revamped Heroes of the Storm 2.0 has implemented a new loot chest system for players to unlock all kinds of items ranging from sprays to legendary skins. However, no one knows what the drop rates for higher rarity items are and publishers can exploit players who spend their hard-earned money in the game. As a result, China proposed that all online gaming companies that has any form of loot system must disclose the drop rate and the regulations has just been passed recently.
The full regulations on online gaming can be found here in the Ministry of Culture of the People's Republic of China webpage, however it is entirely written in Chinese. Fortunately, a NeoGaf user, Chillybright posted a translation in the forum, specifically regarding loot boxes:
2.6 Online game publishers shall promptly publicly announce information about the name, property, content, quantity, and draw/forge probability of all virtual items and services that can be drawn/forge on the official website or a dedicated draw probability webpage of the game. The information on draw probability shall be true and effective.
2.7 Online game publishers shall publicly announce the random draw results by customers on notable places of official website or in game, and keep record for government inquiry. The record must be kept for more than 90 days. When publishing the random draw results, some measures should be taken place to protect user privacy.
Tencent had already disclosed the League of Legends Hextech Chest drop rates even before the law is in effect. Here are the drop rates as published in China's League of Legends website:
The drop rates might or might not be the same for all regions but it is safe to assume that it's similar across all regions since Riot Games is under Tencent.
All other games like Overwatch's and Heroes of the Storm's drop rates are not released by Blizzard yet. But we will all find out about it sooner or later.