Most commercial Internet sites monitor site traffic so that they can recognize attacks by hackers, such as a distributed denial of service attack (DDoS). In this attack, the hacker hijacks a collection of the computers connected to the Internet and has them all attempt to access the commercial site. The sudden increase in activity overloads the server and makes it impossible for legitimate users to log in. The systems engineer says that during typical use, the site gets 20 hits per minute, on average. He didn’t have any idea when asked about a standard deviation. These data show the number of hits per minute over three hours one day, from 7:30 to 10:30 A.M.
(a) Group the data into 15-minute periods and generate X-bar and S-charts with control limits at ± 3 SE. Is the process under control?
(b) Describe the nature of the problem found in the control charts. Do the data suggest that a DDoS attack is happening?