Online service providers are engaged in constant conflict with miscreants who try to siphon a portion of legitimate traffic to make illicit profits. We study the abuse of “trending” search terms, in which miscreants place links to malware-distributing or ad-filled web sites in web search and Twitter results, by collecting and analyzing measurements over nine months from multiple sources. We devise heuristics to identify ad-filled sites, report on the prevalence of malware and ad-filled sites in trending-term search results, and measure the success in blocking such content. We uncover collusion across offending domains using network analysis, and use regression analysis to conclude that both malware and ad-filled sites thrive on less popular, and less profitable trending terms. We build an economic model informed by our measurements and conclude that ad-filled sites and malware distribution may be economic substitutes. Finally, because our measurement interval spans Februa...