Traceroute IP paths are often used in studies of Internet topology and routing. Though producing one of the best available router-level maps of forward paths, traceroute is susceptible to several types of inaccuracies. However, no one to date has quantified the magnitude of these inaccuracies in real-world traceroute paths. We make an initial attempt by reporting on the observed frequency of one type of inaccuracy---third-party addresses. A third-party address is the address of a router interface that does not lie in the actual path taken by packets. Based on an examination of thousands of traceroute paths from six locations worldwide and the application of several metrics, we find that the situations in which third-party addresses can occur to be relatively uncommon. They mostly occur within a few hops of the destination (that is, at the destination edge of the network), with multihoming being their most likely cause. Our conclusion is that third-party addresses cannot be a significant source of AS map distortions.