Brakes suddenly failed

1995-Hyundia-Accent-100900.01 miles: The brake pedal lost all resistance & went straight to the floor when I stepped on the pedal. I pumped them 3-4 times & the pedal came up partially. I had to use the emergency brake to avoid from crashing on the freeway. What could be the reason for the lose of pressure or(whatever it's called) in the brakes? It just seems odd, especially since I keep my car serviced regularly, It just had a full tune-up at the dealers & I requested for the brakes to be inspected do to a noise. They said it needed a rear brake kit, other than that the brake system was fine & this was just 4 months ago. What hold cause such a dangerous condition in such a short period of time. Thank you for your time & it is greatly appreciated, Sincerely, AntoinetteDF