Insurers/Manufacturers are responsible for accidents. Up to them to decide if the vehicle was at fault or not. Vehicle "operator" is responsible for driving offences, in this case the vehicle/software manufacturer.
If malicious changes to speed limits are identified then criminal proceedings are warranted against those who are making the changes. Likewise for anyone who hacks their/other cars systems.
An autonomous vehicle should be capable of being a better driver than 99% of the population w.r.t. observing and obeying the laws of the road. GPS information should be enough if ALL roadworks have to be added to the database BEFORE any works commence. Variable speed limits can be set to communicate with the vehicle so it knows what the speed limits ahead are and can respond appropriately.
Everyone keeps on about the what-ifs. I'd be amazed if even the current systems weren't 1,000,000% better drivers than most of the feckwits currently supposed to be in control of their 1+ Ton lethal weapons, and that probably does include me and you! :-)