1st. - Go to Youtube and find the Video you want lets say I want John, by: Lil Wayne i go and find the video i want and "COPY" the URL of the video
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2nd. - Go to http://keepvid.com/ and find the bar in the middle of the screen that says "DOWNLOAD" at the end
3rd. - "PASTE" your URL into the bar and push download. *NOTE: You need JAVA for this to work and you don't download anything!* It will ask you to trust and run the program click trust and run.
4th. - It Will ask you what do you want to save this as? like:
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5th. - Click the type you want to download
6th. - Select Where you want it to go
7th. - Rock out to your fully and virus-free youtube downloads!
*Note: I know it asks to trust the program but i've been using this for about 4 years and i never once heard or have even ever seen a virus from Keepvid.