Invalid traffic refers to any activity that does not come from a genuine user with a real interest in the ad. It can include the following:    – Spam clicking caused by malware – Spam clicking by competing advertisers – Activity from paid click farms – Clicks from fraudulent placings such as ad stacking – Botnets – Accidental clicks from poorly placed ads   If not detected and filtered out, invalid traffic can affect data accuracy and reduce your return on ad spend.