Most books available for download at "non-official" sites (i.e. not the sites of the publishers) are protected by copyright. This holds for practically all books by Springer, Oxford Univ. Press, etc. However, some publishers (especially institutes, universities, academies and similar) provide open-access books.
In a matter of fact, in Europe as well as in the US, almost all academic books are published outside of the open Access system. This means that you cannot officially upload them. In many European countries, for example, in Poland and Germany, you can download them for private use. It is not prohibited by law even if they were not legally uploaded, except for Torrent, what is recognised as an illegal system of distribution is not prohibited by law.