A personal firewall might be a good contribution to security. Yet, if you do
not understand much about the topic, then you are likely to be confused and
misled by its alerts and queries, and thus find yourself spending hours in
chasing after imaginary crackers, fear from imaginary threats, and misconfigure
it due to misunderstanding. You may find yourself blocking legitimate and
important communication believing it to be cracking efforts, and thus surprised
to see why things work slowly or why you are disconnected from the Internet, or
you might be misled to allow a non-legitimate communication by some software
that tricked you to believe that it is a legitimate one. On the other side, if
you are quite knowledgeable on computers and security, then you are likely to
effectively defend your computer even without a firewall (by means discussed in
section II.4) and it is thus that the role of personal firewall in securing
your computer, is extremely small and not much important. We discuss here in
brief some of the problems that personal firewalls may generate.
A False Sense of Security
As we've already learned here, a firewall is limited in its ability to secure your computer. Yet, many people believe that if they will install a personal firewall they will be secured against the various security threats. I was even surprised to find out that there are people who believe that give much higher priority in installing a personal firewall than in installing an antivirus program. An always updated antivirus program plays a much more important role in the security of a personal home computer than installing and maintaining a personal firewall. A personal firewall should not come on account of any other security measure that you use.
A False Sense of Insecurity
When you install a firewall and you look at all the communication efforts through it, you might be surprised at the amount of communication efforts from the Internet to your computer. Most of them are blocked by a typically configured firewall. There are all the times efforts to try to communicate with various backdoor Trojans on your computers. If you are not infected, there will be nothing to listen and to respond to those communication efforts, and they are thus practically harmless. There are efforts to communicate with your NBT driver, to see if your computer by mistake allows file sharing. There are other types of probes to see if your computer exists, or various efforts of servers to probe your computer in order to find the best path for legitimate communication to it. There are sometimes remnants of communications that were supposed to go to other computers, but made their way to yours (for advanced readers: because the IP number that your computer uses, were used by some other computer earlier). Those communication efforts are blocked even without a firewall. If your computer is not infected with a RAT, and if your computer don't have NetBIOS over TCP/IP enabled or even it does not have file and print sharing enabled (and on most computers this is disabled by default), then none of these pose any security threat. If your computer is not infected with a SubSeven Trojan, then no matter how often there will be efforts to communicate with it, they are all doomed to be failed.
Yet, some personal firewall (such as Norton Personal Firewall or ZoneAlarm) by default proudly announce that they have just blocked an effort to crack into your computer. Norton may even define those efforts that were blocked as "high security threats" while they were not a threat at all even if your computer didn't have a personal firewall at all. Such firewalls give you the false impression that they save your computer again and again from extremely dangerous threats on the Internet, so that you wonder how did you survive so much time without noticing any intrusion before you installed the firewall. I usually say, that those personal firewalls are set their "report level" to "promotional mode". Namely, the personal firewall is set to give you the false impression that it is much more important than it really is.
Chasing After Ghosts
This is a side effect of the types of misunderstandings that were discussed in the previous subsection.
When a person who starts to learn about the jargon related to personal firewalls, is reported that some "dangerous" communication efforts persist from the same source, the person is decisive to locate and identify the "hacker", and perhaps report about it to the police or to its Internet service provider. However, since many people do not really understand thoroughly how things work, they may sometimes spend many hours in trying to locate a cracker that does not exist, or when the knowledge they need to have, in order to track the cracker, is much higher than what they have, and they might even suspect the wrong person due to lack of knowledge (e.g. the connection person on the Internet service provider that was used by the cracker). More knowledgeable people, usually do not bother to track those "hackers" (which are usually teenagers), but instead are concentrating on the security of their computer.
Blocking Legitimate Communications
No personal firewall is smart enough to decide for the user what is a legitimate communication and what is not. A personal firewall cannot make a distinction between a legitimate program trying to contact its server to check and notify the user when there is a newer version, and a non-legitimate program trying to communicate with its server in order deliver sensitive information such as passwords, unless the user tells it. It is thus up to the user to decide what should be considered as legitimate and what should not. Yet, can we count on the user to be knowledgeable enough to decide what is legitimate and what is not? In many cases the user is not knowledgeable enough, and may thus allow non-legitimate communication or disallow a legitimate and important communication. There are many types of communications handled just to manage other communications. Among this are various types of communications between your computer and the various servers of your Internet service provider. A not knowledgeable user may interpret those types of communications as cracking efforts, and will thus decide to block them. As a result, a connection might become slower, a connection to the Internet service provider might be disconnected quiet often and other types of communication problems.
Being Tricked by Trojans bbb
Just as less knowledgeable users may instruct the firewall to block legitimate communications, they can be tricked by various Trojans to allow them to communicate. Some Trojans are using names resembling or identical to names of legitimate programs, so that the user would think that it is a legitimate programs. Users should be aware of that.
Heavy Software, Buggy Software
Until now we discussed only problems related to lack of appropriate knowledge by the user. Yet, there are other problems regarding personal firewalls. For example, some of them are known to be quite heavy on computer resources, or slow down the communication speed. Different personal firewalls quite vary with regard to that. If you have a new computer with a slow Internet communication (such as regular dial-up networking) then it might not slow down your computer noticeably. Yet, if you use an older computer, and a fast communication, you might find that some personal firewalls will slow down your communication quite drastically. Personal firewalls also vary on how much they are stable.
Advantages of External Firewalls over Personal Firewalls
1. They do not take resources from the computer. This should be clear. This is especially useful when the firewall blocks flooding attacks.
2. It is harder (although in principle still possible) for a Trojan horse to disable it, because it does not reside in the same computer that the Trojan has infected. It is not possible to use the specific communication while totally bypassing the firewall.
3. They can be used without any dependence on the operating system on the computer(s) they defend.
4. No instability problems.
A False Sense of Security
As we've already learned here, a firewall is limited in its ability to secure your computer. Yet, many people believe that if they will install a personal firewall they will be secured against the various security threats. I was even surprised to find out that there are people who believe that give much higher priority in installing a personal firewall than in installing an antivirus program. An always updated antivirus program plays a much more important role in the security of a personal home computer than installing and maintaining a personal firewall. A personal firewall should not come on account of any other security measure that you use.
A False Sense of Insecurity
When you install a firewall and you look at all the communication efforts through it, you might be surprised at the amount of communication efforts from the Internet to your computer. Most of them are blocked by a typically configured firewall. There are all the times efforts to try to communicate with various backdoor Trojans on your computers. If you are not infected, there will be nothing to listen and to respond to those communication efforts, and they are thus practically harmless. There are efforts to communicate with your NBT driver, to see if your computer by mistake allows file sharing. There are other types of probes to see if your computer exists, or various efforts of servers to probe your computer in order to find the best path for legitimate communication to it. There are sometimes remnants of communications that were supposed to go to other computers, but made their way to yours (for advanced readers: because the IP number that your computer uses, were used by some other computer earlier). Those communication efforts are blocked even without a firewall. If your computer is not infected with a RAT, and if your computer don't have NetBIOS over TCP/IP enabled or even it does not have file and print sharing enabled (and on most computers this is disabled by default), then none of these pose any security threat. If your computer is not infected with a SubSeven Trojan, then no matter how often there will be efforts to communicate with it, they are all doomed to be failed.
Yet, some personal firewall (such as Norton Personal Firewall or ZoneAlarm) by default proudly announce that they have just blocked an effort to crack into your computer. Norton may even define those efforts that were blocked as "high security threats" while they were not a threat at all even if your computer didn't have a personal firewall at all. Such firewalls give you the false impression that they save your computer again and again from extremely dangerous threats on the Internet, so that you wonder how did you survive so much time without noticing any intrusion before you installed the firewall. I usually say, that those personal firewalls are set their "report level" to "promotional mode". Namely, the personal firewall is set to give you the false impression that it is much more important than it really is.
Chasing After Ghosts
This is a side effect of the types of misunderstandings that were discussed in the previous subsection.
When a person who starts to learn about the jargon related to personal firewalls, is reported that some "dangerous" communication efforts persist from the same source, the person is decisive to locate and identify the "hacker", and perhaps report about it to the police or to its Internet service provider. However, since many people do not really understand thoroughly how things work, they may sometimes spend many hours in trying to locate a cracker that does not exist, or when the knowledge they need to have, in order to track the cracker, is much higher than what they have, and they might even suspect the wrong person due to lack of knowledge (e.g. the connection person on the Internet service provider that was used by the cracker). More knowledgeable people, usually do not bother to track those "hackers" (which are usually teenagers), but instead are concentrating on the security of their computer.
Blocking Legitimate Communications
No personal firewall is smart enough to decide for the user what is a legitimate communication and what is not. A personal firewall cannot make a distinction between a legitimate program trying to contact its server to check and notify the user when there is a newer version, and a non-legitimate program trying to communicate with its server in order deliver sensitive information such as passwords, unless the user tells it. It is thus up to the user to decide what should be considered as legitimate and what should not. Yet, can we count on the user to be knowledgeable enough to decide what is legitimate and what is not? In many cases the user is not knowledgeable enough, and may thus allow non-legitimate communication or disallow a legitimate and important communication. There are many types of communications handled just to manage other communications. Among this are various types of communications between your computer and the various servers of your Internet service provider. A not knowledgeable user may interpret those types of communications as cracking efforts, and will thus decide to block them. As a result, a connection might become slower, a connection to the Internet service provider might be disconnected quiet often and other types of communication problems.
Being Tricked by Trojans bbb
Just as less knowledgeable users may instruct the firewall to block legitimate communications, they can be tricked by various Trojans to allow them to communicate. Some Trojans are using names resembling or identical to names of legitimate programs, so that the user would think that it is a legitimate programs. Users should be aware of that.
Heavy Software, Buggy Software
Until now we discussed only problems related to lack of appropriate knowledge by the user. Yet, there are other problems regarding personal firewalls. For example, some of them are known to be quite heavy on computer resources, or slow down the communication speed. Different personal firewalls quite vary with regard to that. If you have a new computer with a slow Internet communication (such as regular dial-up networking) then it might not slow down your computer noticeably. Yet, if you use an older computer, and a fast communication, you might find that some personal firewalls will slow down your communication quite drastically. Personal firewalls also vary on how much they are stable.
Advantages of External Firewalls over Personal Firewalls
1. They do not take resources from the computer. This should be clear. This is especially useful when the firewall blocks flooding attacks.
2. It is harder (although in principle still possible) for a Trojan horse to disable it, because it does not reside in the same computer that the Trojan has infected. It is not possible to use the specific communication while totally bypassing the firewall.
3. They can be used without any dependence on the operating system on the computer(s) they defend.
4. No instability problems.
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