How to use the ALT key in a Virtual Box guest session?

5chdn's solution is too cumbersome. Instead of Alt, use Win+Alt in guest and you're done.

For example, to use Rubymine's multiple caret mode, original shortcut is Alt+click, which becomes Win+Alt+click. Easy peasy.

This worked for me finally:

The ALT key works within the virtual box guest session if you run it in fullscreen without mouse integration.

• HOST+I disables the mouse integration.
• HOST+F switches to fullscreen.

Hit HOST+I and HOST+F again to return to your host system.