It turned out that vulnerabilities in Image Uploader caused not just killbit problem, but it led to one more aftermath. We are getting more and more complaints from our customer that end users experience issues with Image Uploader if they have Norton Antivirus installed.
After some investigations we found out that Symantec especially included Image Uploader to the threat list in one of their updates. And perhaps unlike killbit, Norton affects new secure version.
I have just posted my suggestions how to handle this to Image Uploader FAQ forum:
We will definitely make some more detailed investigations on this (what exact builds are affected, etc) and publish additional information in that post. Also, we are going to contact Symantec and try to come to some solution.