Malvertising
Websites or web publishers unknowingly incorporate a corrupted or malicious advertisement into their page. Computers can become infected pre-click and post click. It is a misconception that infection only happens when visitors begin clicking on a malvertisement. "Examples of pre-click malware include being embedded in main scripts of the page or drive-by-downloads. Malware can also auto-run, as in the case of auto redirects, where the user is automatically taken to a different site, which could be malicious. Malware can also be found in the delivery of an ad – where a clean ad that has no malware pre or post click (in its build and design) can still be infected whilst being called. Malicious code can hide undetected and the user has no idea what's coming their way. A post-click malvertisement example: "the user clicks on the ad to visit the advertised site, and instead is directly infected or redirected to a malicious site. These sites trick users into copying viruses or spyware usually disguised as Flash files, which are very popular on the web." Redirection is often built into online advertising, and this spread of malware is often successful because users expect a redirection to happen when clicking on an advertisement. A redirection that is taking place only needs to be co-opted in order to infect a user's computer.
MindGeek
It was reported in April 2013 that visitors to some of the world's most popular (by Alexa rank) pornography sites risked malware being installed on their machines by malicious third party advertisements. The claims were made by security researcher Conrad Longmore, who writes a blog on malware, spam and scams. Longmore's figures were collected using Google Safe Browsing Diagnostics, which looks for harmful content on websites, and the statistics for two sites; xHamster and Pornhub were published by BBC News. The BBC article stated that based on Longmore's research, 5% of pages on xHamster (which has never been owned by Mindgeek / Manwin), and 12.7% of pages on Pornhub incorporated malvertising. MindGeek (still known as Manwin at the time) said in a statement that their own figures showed that 0.003% of the advertisements they served over the period that Longmore's data was collected contained malware, and they said that the advertisements they serve are monitored for malware and malware is immediately removed.