Suppose you are computer security expert working for a major company, CableClock, any you have just discovered that many of the computers at CableClock are infected with malware that must have come from users visiting unsafe websites. For each infected computer, you are given a log file that lists all websites it has visited since the last time it was scanned for malware. Unfortunately, as you look over these log files, you notice that there isn’t a single website that they all visited. You conclude, therefore, that there must be a number of websites that are able to inject this malware, and the most likely candidates would be in a smallest collection that is visited by all the infected computers. Show that the decision version of the problem of determining such a collection is NP-complete.