单项选择题 Which of the following is a sign that a computer has been infected by a worm?（）

单项选择题 Users in the office report that the speed of the Internet has drastically decreased since the recent network hardware refresh. Which of the following could be attributed to the problem?（）

多项选择题 For added security, a network administrator has decided to lock down the wireless network. Which of the following are ways to accomplish this? （）(Select TWO).