I'm trying to make some modifications to a wordpress multisite and i could use some help from someone more experienced. I want to restrict the acces to my blogs unless the user has an account. In detail : i have a series of blogs, each one with an admin/autor. If a user wants to read posts from a blog, he should first go on the main site, to wp-signup.php and create an account. I'm planning on creating a plugin, active on all subsites. Is this possible? if yes, could someone give me some directions - wich hooks, filters and functions i would need ?