How to find MACHOs in the Virgo Cluster
  We discuss the feasibility of finding extra-galactic MACHOs by monitoring quasars behind the Virgo cluster of galaxies. We show that with only a modest observing programme one could detect several MACHOs in the mass range 1 X 10^{-5} to 2 X 10^{-2} solar masses if they make a significant contribution to the mass of Virgo. The contamination by events from cosmologically distributed MACHOs is estimated and is negligible if either the MACHO mass is greater than about 10^{-4} solar masses or the quasar radius is greater than about 3 X 10^{15} cm. 
Helen Tadros, Stephen Warren, Paul Hewett