The OpenX Ad Server (2.8.10) backdoor allows an attacker to execute any PHP code via the “eval” vulnerability. The vulnerability only applies to the free downloadable open source product, OpenX Source. All of OpenX’s main suite of products, including OpenX Enterprise (ad serving), OpenX Market (exchange) and OpenX Lift (SSP) are not affected. Last year in March 2012, it was hacked and served malwareusers.users.org.
Source: https://thehackernews.com/2013/08/OpenX-Advertising-Malware-backdoor-hacked-trojan.html