This will be a dump of various bits and pieces of miscellaneous decking knowledge.
1. Canonically the Matrix requires a subscription to use. Because you're a fly-by-night shadowrunner who refuses to pay the corps their nuyen, not that you have a SIN to pay with, *any* intrusion into the Matrix is considered a hostile one. This means as soon as you step foot into it the tally (security/alert) level begins to climb.
2. Exits themselves (SANs) can be encrypted and there are several bugs on how it is documented.
locate host blah
→ Your search returns the address blah.
logon blah
→ You fail to gain access to the host.
# The target room has an AccessScramble value, which blocks remote login. But it could be the source room blocking, so…
analyze access
→ There is nothing out of the ordinary about that subsystem.
# Well, now what? (This is what usually keeps people from logon. But the source room has no encryption. So decker has bright idea:)
analyze blah
→ Analyze what? (That doesn't work…)
help decrypt
→ helpfile shows no ability to decrypt exits/SANS exists
# But finally if you just do it anyway:
decrypt blah
→ You successfully decrypt that SAN.
So, the room is not the SAN, the exit is. An access-encrypted room can prevent movement in, forcing you to decrypt it blind.