The ArcheAge Forums have an explanation from Trion Worlds for why some ArcheAge players have lost some gold, revealing they've been revoking what they are calling "illicit gains" in the MMORPG (thanks Massively). Here's what's happened:

A number of you have mentioned that you're seeing gold disappearing.

As we broadcasted in yesterday's initial blast of rapturing hackers, gold farming bots, mules, and storage accounts, we're now also taking the step of removing the gains passed on by them.

What that means is: If you bought or were gifted gold from one of them, you may see it disappear. We do have the ability to trace coin, and that's the gold that's being cleaned up right now.

The best bet is to not buy gold - It's the same people trying to crap up chat with spam and trying to fill the game with bots and landgrabs. If you bought gold from one of those sites, you are absolutely welcome to try to go back to them for a refund, but we will not be returning gold purchased or gifted from goldsellers and botters. It's off in the ether from whence it came.