In Microsoft Sql it is possible to encrypted stored procedures with
CREATE PROCEDURE dbo.foo
WITH ENCRYPTION
AS
BEGIN
SELECT \'foo\'
END
You can not do this in MySQL. See bug #4210.
[Edit]: The comment from Leonidas on another answer to this question needs to be out there for anyone to read, so I'm quoting it here:
Obfuscation can be reversed. I found at least one product via Google, that promises to reveal the SP-code. So I think/hope that the MySQL-team won't bother with "security by obscurity" or even worse "intellectual asset protection" (as described in the bug 4210).
It looks like its been requested before but I don't know if they're considering it.