  We define the hitting (or absorbing) time for the case of continuous quantum
walks by measuring the walk at random times, according to a Poisson process
with measurement rate $\lambda$. From this definition we derive an explicit
formula for the hitting time, and explore its dependence on the measurement
rate. As the measurement rate goes to either 0 or infinity the hitting time
diverges; the first divergence reflects the weakness of the measurement, while
the second limit results from the Quantum Zeno effect. Continuous-time quantum
walks, like discrete-time quantum walks but unlike classical random walks, can
have infinite hitting times. We present several conditions for existence of
infinite hitting times, and discuss the connection between infinite hitting
times and graph symmetry.
