Examples are always risky. I don't see support for it right now, so my guts say the examples are outdated.
Sounds like Brute Force access right now is the only way access makes OS go up over time.
No, you don't lose the legal access, you simply face OS and consequences of your actions, but the access itself doesn't suddenly trigger alarm bells.
If you're doing a Sleaze/Attack action, and your Attack/Sleaze is higher, you face a dice penalty equal to the difference. Backdoor Entry is Sleaze-based, so for when you're sneaking. So either you're taking a penalty on the Backdoor, or on any Attack-linked actions afterwards. On the other hand, Brute Force is not only better when you're in a rush (combat decking that one round can matter greatly), but also better if you're convinced you're going to end up in a Matrix battle anyway.
For Patrol IC, basically it has 1 Matrix Perception roll-value per minute, and 1 Minor per Round is spent investigating. In a quiet node, it may be constantly scanning you. In a crowded node, likely it will only scan you once per minute. In the end, the exact frequency is up to the GM. It's a new roll every minute, opposed and without Try Again penalty because it's a constant opposed test.
Say there's ten people. It scans everyone twice per minute. The first roll, of let's say 4, applies twice. Then it rolls again.
If it faces just 5 people, probably it scans you 4x per minute. So you resist the same roll 4x over time. Then it rolls again.