there are tons of software out there to use in hiding IP addresses. an IP address is your identity over the internet. let's say you register in a particular website like ebay for example. you can create multiple accounts as you like but they will know that those accounts are owned by only one person because of the IP address, you got the picture.
there is a tool I found here known as "cloakfish", its a piece of shit that hides your ip and you need to purchase it to have a number of different IP to use on a regular basis.
If you are in a hacking world, you can use different methods and other softwares that aren't mentioned in here.
TIP:, some softwares only hides your browsers IP, as far as I know. but there is this nice software that hides your computer's IP in depth. based on past experience, there are some nice coded web applications that can detect your real IP even if you are using a proxy. so I recommend proxifier for that, though it doesn't give you proxy, socks at all, its like a gun that you need to load some bullets. (just google it)