Dive summary: 

• AdWeek gathered 12 industry experts to help identify companies who were responsible for the web crisis of fake traffic and ad sales; the study revealed the six biggest offenders: AdOn, Adknowledge, eZanga, Jema Media, MGID and BlueLink Marketing.
• One example of generating fake web views was with Smartmomstyle.com, that received traffic from Jema and Adknowledge; in one instance the site was delivered to visitors invisibly while they visited another site, meaning the page view was counted but the viewer saw none of the ads that advertisers had paid for viewers to see. 
• Among the respondents, AdOn seemed to have the worst reputation among the vendors; one respondent claimed they dropped the firm after a brief stint in which the traffic data was inconsistent and "wild."

From the article: 

"Yet other vendors don't have much better reps. 'Adknowledge appears to be a total scam that is generating only fake impressions, whereas MGID is a legitimate blog network that seems to be juicing the numbers, maybe through leased bots,' said a DSP exec."