I do know how to reset my RB2011 (with the reset button, or winbox, or the config site).
But even after a reset, files (like backups) remain in the "File" menu of the router.

If files remain there, what else will stay foot in the RouterOS that we cant see?

Is there a way to really, totally reset the routeros?

Netinstall with disk format. Only licence stays on the disk.

Thx, will google on that!

Searching the forum is enough: http://forum.mikrotik.com/viewtopic.php?f=3&t=14415
And reading manual: http://wiki.mikrotik.com/wiki/Netinstall

Thank you. A few more beginners questions will popup the days following...

Search the forum before ask. There is no begginers question that was not answered already . Starting with mikrotik ros means a lot of reading and a lot of tryouts. Really painfull trip will be rewarded by new knowledge gain.