my best guess why VirusScan 8.7 with antispyware does not recognize that kind of trojan would be this: this may be a downloader application (a sneaky undercover front agent) which changes regularly in order to avoid easy detection by AV software. My other guess is that this will always be so.
What in turn never changes much is that what these front agents want to achieve on your computer.
You could hope that sooner or later this downloader file will be incorporated in the signature files, therefore switch on Artemis on higher levels than Low (heuristic network check), make sure you scan everywhere (i.e. no folder exclusions apply to where this piece of code is found).
In parallel I would recommend using Access Protection rules to block those actions that every trojan seems to be fond of performing, like making themselves autorun or planting themselves within device drivers (CLSIDs) - when installing legitimate software this will need to get disabled temporarily or have the installer excluded in this rule.
I recommend using both approach.
(In the meantime if you have access to the actual file not reported to be the malware, please submit to www.virustotal.com to see in what percentage it is detected as malware by other AV engines.)