Threat Detected - hxxp://s.vb3k.com/crossdomain.xml

I started getting this threat alert this morning and it goes off about every 5-10 minutes. I read another thread where a pro user named Valerium (spelling?) gave instructions to another user on how to fix it. I am hoping that he, or something similar, can advise me.

Hi there lets have a look see. Does this only occur with Chrome ?

Please download Farbar Recovery Scan Tool and save it to your Desktop.

Note: You need to run the version compatible with your system. If you are not sure which version applies to your system download both of them and try to run them. Only one of them will run on your system, that will be the right version.

[*]Right click to run as administrator (XP users click run after receipt of Windows Security Warning - Open File). When the tool opens click Yes to disclaimer.
[*]Select additions at the bottom
[*]Press Scan button.

https://dl.dropboxusercontent.com/u/73555776/frst.JPG

[*]It will produce a log called FRST.txt in the same directory the tool is run from.
[*]Please attach both logs generated.

I’m using Firefox. Later today, I upgraded Avast to the latest version and rebooted and it hasn’t happened since. Weird!