INVITATION TO CYBERSECURITY 210 Figure 8.9 Windows Defender Firewall. A blacklist is a list of explicitly denied resources. Any site not on the list is approved. This approach identifies unsafe websites and adds them to the blacklist. Blacklists prioritize costs over security. Because only known unsafe or undesirable websites are added to the list, users never need to visit these sites in order to do their jobs. However, it is likely that there are many bad websites that are not on the list. This opens the door to a user visiting a malicious website and causing a security incident. After the first visit, the website might be added to a list of websites to be vetted, and if so, it could be added to the blacklist to prevent users from navigating to it in the future, but by that time the damage may already have been done. Some smartphone users use whitelists or blacklists to control who can call their phones. If a whitelist is used, only known good callers are allowed through, such as friends and family in their contact list; all other callers are sent straight to voicemail. This eliminates spam phone calls. Spam is an unsolicited and unwanted communication. The downside of this approach is that some important phone calls might be missed. Some callers not in a users’ contacts might have legitimate reasons for calling, such as a company calling to schedule a job interview. If a blacklist is used instead, only certain numbers are sent straight to voicemail and everyone else is allowed through. This can prevent harassing calls from the same number, but since spam phone calls often come from different numbers, adding them to a blacklist is like playing a game of Whac-A-Mole: whenever one number is knocked down, a new number pops up! 8.3 Accounting Authentication and authorization mechanisms work together with accounting. Accounting is recording who did what when. As actions are processed, they can be recorded. This is also known as logging. Logging is recording cyberspace events. Because actions in cyberspace are composed of digital signals processed at incomprehensible speeds (see
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