I appreciate that you brought this to my attention, thank you. You are right to be concerned, you can never be too careful with malware and viruses. Please be assurred that I would never add malicious programs to this site. I have no reason to think that the our server has been hacked but just to be sure there is a full scan running through the server as I type this.
No one else has reported to me that they have experienced any similar problems so my guess is that the problem is with the new software that was recently installed on your computer. It seems that the anti-virus program is misidentifying something as an attempt to infect your computer and the warning it is producing is a false positive.
This is the information that I found about downloader.tibs:
http://vil.nai.com/vil/content/v_139634.htm
N/A. Downloaders are not viruses, and as such do not themselves contain any method to replicate. However they may themselves be downloaded by other viruses and/or Trojans to be installed on the user's system.
Many of these additionally are mass spammed by the author to entice people into double-clicking on them.
Alternatively they may be installed by visiting a malicious web page (either by clicking on a link, or by the website hosting a scripted exploit which installs the Downloader onto the user's system with no user interaction.