While running, Spotify Free opens advertisements automatically to default browser, thus it can be classified adware and malicious software. It started to happen couple days ago and other people have experienced same as well.
I removed whole application from my system. It is sad, because Spotify was the best platform to discover new music, especially electronic music. Hope they repair the program, and keep it secure in the future.
Only relevant other source for music is Digitally Imported Internet radio.