Temporary Internet files are downloaded to speed up your viewing of the internet. Each time you visit a web page temporary files are downloaded so as next time you visit the same site you see it quicker. Some files are used by the site owners to establish who is visiting them and they get a lot of statistics from them. 30gb seems an enormous amount.Are you sure you have your computer set up correctly.
They are usually stored here C:/Windows/temp/temporary intermet files
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