4. Assume a future where security counter-measures against DoS attacks are much more widely implemented than at present. In this future network, anti-spoofing and directed broadcast filters are widely deployed. In addition, the security of PCs and workstations is much greater, making the creation of botnets difficult. Do the administrators of server systems still have to be concerned about, and take further counter-measures against DoS attacks? If not, why not? If yes, what types of attacks can still occur, and what measures can be taken to reduce their impact