Crusader is an adware program that displays advertisements, modifies text in search results, and displays tech support scam alerts. This adware functions by downloading a configuration file that provides rules on how Crusader should operate. Crusader is currently being used to promote tech support scams by injecting fake alerts into web pages that people visit. The program is typically bundled with and installed by free programs that you download from the Internet. If you appear to be affected by this program, you can use the guide to scan your computer for unwanted programs and remove them for free.
Source: https://www.bleepingcomputer.com/virus-removal/remove-crusader-adware