Yeesh. Much to take in here.
1. Chinese hackers are smart enough to circumvent App store security
2. App developers are dumb enough to use unofficial Xcode downloads to create their apps (when Xcode is free and easily available - just why?)
2a. WeChat, one of the biggest Chinese social networks, is one of them - wtf?! How amateur can you get??
3. Apple are clearly going to make some fast changes to the way they check apps uploaded to the store - wouldn't be surprised if it happens within the week; and you can bet that offending app compilers will be warned and then banned
/adjustmytinfoilhat...
Maybe it's been a known hack for a long time? Any agency could have been exploiting this for fun and profit for a long time.