One problem related to computer failure has been reported for the 2008 Toyota Prius. The most recently reported issues are listed below.
On 20 may 2010 at 11,966 miles every brake/stability warning light came on (including the warning for the parking/emergency brake which was not engaged), regenerative braking appeared to have failed, and hydraulic/friction brakes behaved as if abs was acting at a very slow pulse rate, approximately a 5-second cycle. For about 2 seconds during the "off" portion of this cycle the brakes were effectively inoperative, with the parking/emergency brake the only source of braking. This behavior persisted after shutting down and restarting the car. The dealer's service department reported that three errors had been logged: c1247 - stroke sensor c1300 - abs ecu malfunction c2318 - low voltage error resetting the computers cleared the warning indications and restored normal brake system behavior. At my behest, the dealer worked with Toyota engineering to identify why a low voltage would cause a computer failure which could cause substantial loss of braking ability. They kept the car for 8 days but did not appear to complete any sort of root cause analysis of the failure. On 17 December 2012 at 27,324 miles the brakes again failed with the same set of warning lights illuminated. This time, abs does not appear to be active at all. For the first 2-5 cm of brake pedal travel, in the regime where regenerative braking would be active, no braking is evident. As the pedal is further depressed, the hydraulic/friction brakes abruptly engage. Pressing harder does result in increased braking though braking is rough. No pulsation as might be expected from abs was noticed. No attempt was made to brake hard enough to lock up the brakes. The vehicle is currently at the dealer.