the fbi warning is legit- it's what they do when they sieze a website
It's fake...why it's fake or for whatever reason, I cannot say, but it's not a legitimate FBI warning.
Inspect the element or the code for the page...<img src="http://www.extremenastytossers.com/dokumenti/FBI_Seizure.jpg" width="960" height="720" alt="Smile"> That's the image...check the site it's coming from...
I've never been to that site before, but bartertown sounds like a trading website.
Something tells me someone sold an account, and someone else payed for it with illegal money and the website got closed down for being the medium, investigation pending. Or they got a % of the sales and that ended up being illegal money.