I would like to search only for torrents licensed as CC BY. With an advanced search I can specify "Attribution" but it seems to return all licenses with an attribution condition including CC BY-NC, CC BY-NC-ND and so on. Is there any way to limit the results only to CC BY?

Not currently, though it is a feature that could be added in a future update.

Hope it gets added in sometime. Thanks for replying.

This has been added.