Hey, thanks so far for all replies.
It was interesting to know about this thing completelly new to me.
I presume that, as Zombie Queen said, must be a thing from robots plus search engines.
All the others websites, as Art-Ak etc asked me permission long time ago. And the rest was made by me, so no problem.
But there are some websites such Yumusica and clones like this one which seem to be search engines or something.
However, when you download something from them, the mp3 file has a huge number, instead of my name and titles.
It is Last FM the same kind of search engine too? Because i found my tracks there too.
I even found an old track i don't have in my computer anymore so, somehow, it was something positive.
As i said, i'm not mad about it, but i hope not to see people getting money with my free tracks, because they are free.
Have a nice day, guys