Teleport Hack (reddit)
From the daily status update:
Reporting exploits
If you discover an emergency game-breaking or economy-breaking bug, do not exploit it, but please notify us immediately at this email address: exploits (at) arena (dot) net. You may also use this email address to report suspected security vulnerabilities. Thank you to everyone who has sent reports. However, note that we cannot respond individually to emails to this address.
I want to hear on these forms that they are aware of it and working on it. This is by far the most serious issue in the game right now.
They already know about this issue. It has already been posted and that post was locked. ArenaNet wants you to report the exploits not make them public.