En Masse Entertainment has posted a brief note on the TERA site to let players know that a potential in-game chat vulnerability has been discovered thanks to a Reddit post (since removed) on the TERA Reddit. En Masse is working to investigate the issue and are working closely with the development team to track down and close the potential exploit. However, at this time, "there is no evidence that the vulnerability is being exploited in these way or that any player info has been compromised".
Please remember that posting about 3rd party software, hacks, or exploits is against the forum rules. With your continued support we can help prevent the spread of information that may aid users with malicious intent to exploit this or any other vulnerability or source tools that would facilitate it. If you have any information that may be valuable to our continued investigation of this, please PM our staff on the forums directly.
According to the Reddit post (which you can see here), the issue arose from the use of HTML for chat which was determined to be possibly linked to hacking attempts through links placed in chat that then open in browsers.
You can read En Masse's response on the TERA site.
Via Anonymous Tip