Over many years of virus and adware removal I have seen the most common sources of infection are (1) Porn sites (2) social networking sites . Teenagers are attracted to sites that have high risk. Aside from avoiding the websites mentioned you can use Mozilla Firefox or Chrome instead of Internet Explorer as your web browser, this decrease your probability of being infected. If you have young people in the house or want to visit high risk websites; doing your browsing from a Mac, Ipad or Linux PC will dramaticly reduce your risk of infection. Linux is another operating system that runs on PC hardware it is similar to windows and has programs that can do all or most of whatxplorer people need to do. Ubuntu Linux is free download and I am familiar with it's installation. Call me to install it for you. If you have multiple PC's at your house installing linux on one of them for web browsing is recommended.