单选题 Most computer systems are ______ to two different groups of attacks: insider attacks and outsider attacks. A system that is known to be ______ to an outsider attack by preventing ______ from outside can still be vulnerable to the insider attacks accomplished by abusive usage of ______ users. Detecting such abusive usage as well as attacks by outsides not only provides information on damage assessment, but also helps to prevent future attacks. These attacks are usually ______ by tools referred to as Intrusion Detection Systems.

【正确答案】 A

【答案解析】大部分计算机系统都很容易(vulnerable，脆弱的，易受攻击的)受到两种不同类型的攻击：来自内部的攻击和来自外部的攻击。一个系统可能通过禁止外部的访问(access，访问，接入)保证免受外部攻击，对于外部来说是安全的(secure)，但是仍然容易受到因用户授权的(authorized)滥用而引起的内部攻击。检测这种用户授权的滥用和来自外部的攻击，不仅提供能评估损害的信息，而且也助于防止以后再受到攻击。这些攻击通常使用被称为入侵检测系统的工具检测(detected)出来。