Security researchers have shut down a large-scale malvertising operation that used sophisticated techniques to remain undetected for months. The operation, dubbed AdGholas, has been running since at least October 2015. The gang behind it managed to distribute malicious advertisements through more than 100 ad exchanges, attracting between 1 million and 5 million page hits per day. The group used a series of complex checks to ensure that the visiting computers are not virtual machines used by security researchers or by ad networks to discover malware.”]