Tera, a Korean MMO that debuted in the US in 2012, has shut down its in-game chat system after some players discovered a potentially serious vulnerability. According to the players' report (Google docs), Tera's chat interface uses HTML, which people can exploit to blast players with external images and links, as well as to collect people's IP addresses. More importantly, someone truly unethical could use it to spread malware. It's an interesting wrinkle for a game that's been up and running for five years, and it's not entirely clear if its North American publisher, En Masse, has known about the vulnerability before the players published their report.
Source: Reddit, En Masse