This is from the Backdoor.trojan file information you provided in the link --
When Backdoor.Trojan is executed, it may create a copy of itself in the \Windows or the \Windows\System folder. In most cases, it uses one or more of the common loading points to make sure that it runs when you start Windows. For information about common loading points, read one of these documents:
This isn't even a possibility with Java applets. Applet software is forced, by design, to follow very strict security measures, and if software tries to break it it won't be allowed to execute. Our software cannot access your computer's files at all, nor does it try to.
SigmaChat is a simple chat applet. It merely opens a socket to our servers for real-time chat communication. It does not allow people to enter your computer, and it does not attempt to cause any harm to your systems.
Tens of thousands of people use SigmaChat daily. I assure you it is not a virus
, a trojan horse/backdoor, or anything of the like.
In the two years we've been in business, this is the first I've heard of someone worried that our software is a backdoor or virus. Occasionally, internet protection software may complain because a non-standard port is being used, but nothing along the lines of a backdoor utility.