The songs -- 'A Day in Your Life', 'Pain Proof', 'If It's Lovin' On Your Mind' and 'Right Back at Ya' -- were uploaded on SoundCloud out of nowhere, reported Variety online.
Forever was the group's last album, aside from a Greatest Hits compilation album released in 2007.
The Spice Girls, made up of Geri Halliwell, Emma Bunton, Mel C and Victoria Beckham, reunited in 2012 to perform at the closing ceremonies for the London Summer Olympics.