My guess is that whoever made the installer had his computer infected. Not all companies have strict rules about what can be on the computer (or developers choose to not follow them and find ways around their enforcements) and this can be one of the downsides. I can't guess whether they virus-scanned the installation or not because it's quite possible that the trojan was new and not being picked up by scanner when they released the charger.
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My guess is that whoever made the installer had his computer infected. Not all companies have strict rules about what can be on the computer (or developers choose to not follow them and find ways around their enforcements) and this can be one of the downsides. I can't guess whether they virus-scanned the installation or not because it's quite possible that the trojan was new and not being picked up by scanner when they released the charger.
Ok, I found this analysis by Symantec which makes the whole thing less naive than I originally thought: http://www.symantec.com/connect/fr/blogs/trojan-found-usb-ba...
They indicate a Liu Hong seems to have authored the install package. No indication if he was a Energizer employee or not.