On the site's Copyright Complaint Form, it says
'You must remove a song from the computer after listening. If You won't delete files from the computer, You'll break the copyrights protection laws. All the rights on the songs are the property of their respective owners. mp3skull.com is a search engine, but we respect an Copyright Laws. So if You have found a link to an illegal mp3 file please use the form below.'
So does this mean it is legal because they "respect Copyright Laws." Also it says that if you do not delete downloaded music from your computer, you'll break copyright protection laws, but does that mean that if you do delete files it is legal then? When do you have to delete them then? Right away? After a certain amount of time...?