Ask is a toolbar that is usually added to your browser when you install free software. Like many toolbars, in addition to changing your home page and search engine web browser, the Ask Toolbar saves the theme of the sites you visit to offer you subsequently targeted advertisements.
Ask got on your PC after you have installed another free software or add-on that had bundled into their installer this browser hijacker. For example, when you install Java, Ask will install its toolbar, set your browser homepage and your default search engine to ask.com.