[clupprich]

No entirely true: A lot of information is transmitted via AIS these days. For example current water depths (St Lawrence Seaway or on the Danube in Europe) are transmitted and used for navigation on these waterways. You also have the possibility to place a distress signal with AIS, which would quite likely lead to a Search and Rescue operation, costing huge amounts of money and taking away resources from real emergencies.

AIS is directly connected to an ECDIS on a ship's bridge, which is the digital replacement for maritime paper charts. AIS targets are displayed in these ECDIS systems and (see above) in some regions of the world the information shown there is also influenced by AIS data.

Also a lot of ports are using AIS (together with radar) to keep an eye on the traffic - spamming those systems, which is easily possible, would quite likely cause severe troubles for larger ports like London or Los Angeles.

I'm honestly surprised that nobody has yet DoS'd a larger port or other infrastructure.

[nitrogen]

I'm honestly surprised that nobody has yet DoS'd a larger port or other infrastructure.

It's probably because most people don't want to do that. Outside of prisons, a good chunk of human safety relies on the fact that most people would rather preserve their own safety than take away that of others.

[wmoser]

All of the ships that I have been on have the overlay feature on the ECDIS turned off. It tends to make the screen too crowded in busy ports. If the mates need to look at someone's name they just compare the reported position from AIS to position on the RADAR/ECDIS of the ship they are trying to contact.

Also, the AIS data is self reporting so if they forget to change the information then it's useless anyways. I've seen 'anchored' ships driving away at 10 knots.

[bcl]

It is fairly short range. 9600bps @ about 162MHz doesn't travel much further than the curvature of the earth. If you started jamming it the FCC and the Coast Guard would become interested fairly quickly since they now use this as part of the port security system.