Absolutely clean traffic is nearly impossible to achieve. Even if you, as the website owner, are sure that nobody is sending bot traffic to your website, there will still be exceptions, like:
Various antivirus scanners like Google Safebrowsing, which Adscore detects
For the cases where you’re displaying adverts on your website, the advertising network delivering them might employ landing page verification services like GeoEdge, which Adscore detects
When your website is shared on an instant messaging service like Skype, that displays screenshots or images from URLs, the bots fetching the screenshot will be detected as well.
The bottomline is, Adscore will always find that a few percentages of traffic to any website, is in fact Bot Traffic, that’s not a false-positive.