Comment 7 for bug 2047778

Pro is a completely free service for personal and small business use, it gives you security fixes for 25000+ additional packages in universe ... to maintain this, the canonical security team had to be extended .
Maintaining an additional 25k packages comes at a cost, what canonical does here is to make enterprises pay for this additional work to be able to then provide it for free to the community...

To make sure such enterprises do not grab it for free there needs to be a control mechanism in place which is why you need to register to get them.

As of hiding info about open security holes on your system, would you prefer to rather not know that your wordpress install from universe is vulnerable in a way a script kiddie can take over your blog site and show porn pics to the world instead of getting the list of available fixes during updates ? While ubuntus base system is indeed very secure, hiding info about open security holes in additional packages and available fixes for these is surely not a good idea.

I'm sure if anyone has a good suggestion how to better solve the above the Pro team would love to hear about them in the thread at:

https://discourse.ubuntu.com/t/ubuntu-pro-faq/34042