Website infection: JS:Agent-BMD[Trj]

I am a website/forums administrator for a gaming studio. The website is my homepage. Until earlier tonight, it has been clean without any problems. However I just came online to get a notice from my AVAST Free that a “JS:Agent-BMD[Trj]” Infection has been blocked. I cannot open the website nor the forums. After notifying my webtech, he had to take down the website to try rooting it out.

Now what in the Heck is “JS:Agent-BMD [Trj]”? A backdoor trojan some hacker dropped into my website?

Now what in the Heck is "JS:Agent-BMD [Trj]"? A backdoor trojan some hacker dropped into my website?
something like that https://www.virustotal.com/nb/file/1bdc1b3fde8efff5cbce5797d859dc6eabfafa6d8355c20a867a5eb8a40eb5b6/analysis/

you can check your site here http://sitecheck.sucuri.net/ / http://killmalware.com/

Hi Pondus,

Here we see that Avast has a very good detection rate for these forms of shell PHP abuse:
http://support.clean-mx.com/clean-mx/md5.php?Sophos=Troj/PhpShell-C
How to find a backdoor and fix it: http://www.wpbeginner.com/wp-tutorials/how-to-find-a-backdoor-in-a-hacked-wordpress-site-and-fix-it/
link article authors are led by Syed Balkhi.

polonus