Well, if you've seen the movie 28 Days Later, you already know---living zombies infected by a rage virus who can actually RUN! And the fact that these zombies aren't undead actually makes them scarier because this is the type of zombie that can exist in real life.
And what's more scarier than that? The "contagious infected" we see in our FDO's book Contagious. These aren't mindless zombies---they have all of their intelligence and can pretend to be normal. But they are nothing at all like their former selves and would gladly kill off their nearest loved ones to achieve the ends of their triangle hosts.
Can't wait to see how this ends! (Although I already know---I peeked at the ending.) 70% of the way through and hopefully I will be finished by the end of the weekend.