ok remember that 99.9% of internet users DONT use and have never used AOL or yahoo. US ISP are a mere drop in the bucket in the world of internet and computers. Although you can have a browser which is has advertising for your isp, you can do what most do and have one without. There are many types out there and the most commonly used would be internet explorer, Netscape, Mozilla firefox and opera. These are the most common but there are undoubtedly more out there. You dont buy them, you can download from the internet.
As someone said, it is very important that you have a good antivirus and firewall, use the window firewall if you are using a MS operating system and a good reputable AV program. I cannot recommend the one I use as its not available for public sale.