Section 5 then continues with an application of the base rate fallacy to the intrusion detection problem, given a set of reasonable assumptions. Jul 07, 2008 base rate fallacy in assessing a situation, an analyst sometimes has two kinds of evidence availablespecific evidence about the individual case at hand, and numerical data that summarize information about many similar cases. Terrorists, data mining, and the base rate fallacy. They focus on other information that isnt relevant instead. Abnormal patterns of reference to programs or data. Ieee transactions on software engineering, 199, september, 1993. The base rate fallacy and its implications for the difficulty of intrusion detection the base rate fallacy and its implications for the difficulty of intrusion detection stefan axelsson presented by kiran kashalkar. The baserate fallacy and its implications for the dif. The baserate fallacy provides two lessons when considering an idps.
Suppose that the rate of disease d is three times higher among homosexuals than among heterosexuals, that is, the percentage of homosexuals who have d is three times the percentage of heterosexuals who. Suppose further an intrusion detection system generates 1,000,100 log entries. Base rate fallacy news and updates from the economic times. The classic scientific demonstration of the base rate fallacy comes from an experiment, performed by psychologists amos tversky and daniel kahneman, in which participants received a description of 5 individuals apparently selected at random from a pool of descriptions that contained 70 lawyers and 30 engineers, or vice versa. Sep 24, 2019 base rate fallacy, or base rate neglect, is a cognitive error whereby too little weight is placed on the base original rate of possibility e. Typically, the volume of packet data in a network is enormous on the order of tens of millions of packets per day and. The baserate fallacy and its implications for the difficulty. A strict anomoly detection model for intrusion detection systems the baserate fallacy is one of the cornerstones of bayesian statistics, stemming from bayes theorem that describes the relationship between a conditional probability and its opposite, i. Understanding these probabilities enables us to evaluate the claims of many types of security technologies, including the effectiveness of antivirus software, web application scanners, and ids ips systems. The base rate fallacy and its implications for the difficulty of intrusion detection stefan axelsson department of computer engineering chalmers university of technology gsteborg, sweden email. This paper aims to demonstrate that, for a reasonable set of assumptions, the false alarm rate is the limiting factor for the performance of an intrusion detection system. An ips intrusion prevention system is a network ids that. An ips intrusion prevention system is a network ids that can cap network connections.
The base rate fallacy information security needs to. If there are too many false positives, the analyst is not. People often focus on specific information that only relates to a certain case and as a result sometimes jump to inappropriate conclusions. Pdf the baserate fallacy and its implications for the.
Gigerenzers natural frequencies technique for avoiding the base rate. If there are too many false positives, the analyst is not able to find the real intrusions in the alert traffic. False positivesthat is, the idps alerts on benign trafficare impossible to avoid. Feb 02, 2014 those who do so commit the base rate fallacy. The baserate fallacy and its implications for the difficulty of. This is due to the base rate fallacy phenomenon, that in order to achieve substantial values of the bayesian detection rate pintrusionalarm, we have to achieve a perhaps in some cases unattainably low false alarm rate.
This is due to the baserate fallacy phenomenon, that in order to achieve substantial values of the bayesian detection rate, p intrusion j alarm, we have to achievea perhaps unattainably lowfalse alarm rate, on the order of 1 10 5,or 100. An intrusion detection system should recognize a substantial percentage of intrusion while maintain the false alarm rate at acceptable level 4. Another practical application for base rate fallacy give them 33% and tell them its 50% lots of food companies exploit the base rate fallacy on their packaging. This is due to the baserate fallacy phenomenon, that in order to achieve substantial values of the. Citeseerx the baserate fallacy and the difficulty of. In what follows, section 4 gives a description of the base rate fallacy. The base rate fallacy or why antiviruses, antispam filters and detection probes work worse than what is actually promised elevenpaths 17 march, 2019 before starting your workday, while your savoring your morning coffee, you open your favorite cybersecurity newsletter and an advertisement on a new intrusion detection system catches your attention. An intrusion detection system ids is a device or software application that monitors a network or systems for malicious activity or policy violations. The final problem that idpss encounter is that they are trying to find inherently rare events. Credit firms can keep ratings pat for borrowers anyone who has not been able to pay because of the moratorium, we have taken care to not report them to rating agencies, yes bank managing director prashant kumar said. Citeseerx document details isaac councill, lee giles, pradeep teregowda. A siem system combines outputs from multiple sources and. May 03, 20 understanding these probabilities enables us to evaluate the claims of many types of security technologies, including the effectiveness of antivirus software, web application scanners, and ids ips systems.
First, when an idps advertises its falsepositive rate as reasonable, keep in. Base rate fallacy or base rate neglect is the tendency to mistakenly estimate the likelihood of an event without taking account of all the relevant data e. This type of numerical information is called a base rate or prior probability. The base rate fallacy reminds me of the prosecutors fallacy. The base rate fallacy that finds too many terrorists. Sep 08, 2017 those who do so commit the base rate fallacy. The base rate fallacy and its implications for the difficulty. Catchup requires a neverbefore seen gdp growth of 8. A strict anomoly detection model for intrusion detection. Typically, the volume of packet data in a network is enormous on the order of tens of millions of packets per day and only a few might involve any activity related to intrusion. Then i point out just how much higher the accuracy of the always guess the more likely outcome screening actually is. The base rate would be 1 terrorist per 300,000 people. Therefore, intrusion detection systems ids have been introduced as a third line of defense.
Firewalls, tunnels, and network intrusion detection. Base rate is an unconditional or prior probability that relates to the feature of the whole class or set. This huge difference can results in the generation of multitudes of false alarms. With the bayesian detection rate and the baserate fallacy in mind, lets discuss the system architecture of a network ids. This is due to the baserate fallacy problem, because of which the factor limiting the performance of an intrusion detection system is not the ability to identify behavior correctly as intrusive, but rather its ability to suppress false alarms.
The baserate fallacy and its implications for the difficulty of intrusion detection stefan axelsson department of computer engineering chalmers university of technology gsteborg, sweden email. The base rate fallacy will be explained and demonstrated. Suppose that nsa surveillance has an accuracy rate of. The goal is to find the probability that the driver is drunk given that the breathalyzer indicated heshe is drunk, which can be represented as. The base rate fallacy can be explained in false positive false negative. On the concept of base rate fallacy, there seems to be a very large difference between the amounts of events seen as normal and the amount of intrusion events, which are very few. How the baserate fallacy affects ids was already advised.
Base rate fallacy, or base rate neglect, is a cognitive error whereby too little weight is placed on the base original rate of possibility e. This is due to the baserate fallacy phenomenon, that in order to. The base rate fallacy or why antiviruses, antispam filters. You may recall having heard this statistic before, or. The techniques classically applied within ids can be subdivided into two main categories. When something says 50% extra free, only a third 33% of what youre looking at is free. If you think half of what youre looking at is free, then youve committed the base rate. The baserate fallacy and its implications for the difficulty of intrusion. Turning the sensitivity down to turn down the fp noise will result in a higher fn, which is to say a lower. The base rate fallacy is related to base rate, so lets first clear about base rate. The base rate fallacy and the confusion of the inverse fallacy are not the same. On the scalability of security in largescale software systems.
The base rate fallacy and its implications for the difficulty of. The base rate fallacy example base rate of disease is 110,000 a test is 99% accurate on 100 people with the disease, 99% of the tests would report positive on 100 people without the disease, 99% of the tests would report negative when the test result is positive what is the probability of your having the disease. If you overlook the baserate information that 90% and then 10% of a population consist of lawyers and engineers, respectively, you would form the baserate fallacy that someone who enjoys physics in school would probably be categorized as an engineer rather than a lawyer. If the base rate is known, then a fourfold table, also called a 2 x 2 table or matrix, is a mechanism that helps us understand the correct probabilities of true positive, false positive, true negative, and false negative events and avoid the base rate fallacy. This is due to the baserate fallacy phenomenon, that in order to achieve. The base rate fallacy and its implications for the. What is the difference between a distributed hostbased ids and a nids. Only 100 of the 1,000,100 entries correspond to actual malicious events. We estimate 4% permanent loss to real gdp from the decadal trend levels in the base case crisil said. Bayestheorem and baserate fallacytheorem and baserate fallacy 3. The baserate fallacy and the difficulty of intrusion detection. Execution mon itoring of securitycritical programs in distributed sys.
Terrorists, data mining, and the base rate fallacy schneier. This is due to the base rate fallacy problem, because of which the factor limiting the performance of an intrusion detection system is not the ability to identify behavior correctly as intrusive, but rather its ability to suppress false alarms. Example suppose an ids is 99% accurate, meaning a 1% chance of false positives or false negatives. Statistical foundations of audit trail analysis for the detection of computer misuse. This chapter demonstrated that intrusion detection in a realistic setting is harder than was perhaps thought. Logical fallacy formal fallacy probabilistic fallacy the base rate fallacy alias. A strict anomoly detection model for intrusion detection systems the base rate fallacy is one of the cornerstones of bayesian statistics, stemming from bayes theorem that describes the relationship between a conditional probability and its opposite, i. In what follows, section 4 gives a description of the baserate fallacy. Mar 17, 2019 the base rate fallacy or why antiviruses, antispam filters and detection probes work worse than what is actually promised elevenpaths 17 march, 2019 before starting your workday, while your savoring your morning coffee, you open your favorite cybersecurity newsletter and an advertisement on a new intrusion detection system catches your attention. If the base rate is known, then a fourfold table, also called a 2 x 2 table or matrix, is a mechanism that. Many different demands can be made of intrusion detection systems. On the concept of baserate fallacy, there seems to be a very large difference between the amounts of events seen as normal and the amount of intrusion events, which are very few. The baserate fallacy and the difficulty of intrusion.
In other words, the defensivefailure rate and the usagefailure rate are both 0. A strict anomoly detection model for intrusion detection systems. If you overlook the base rate information that 90% and then 10% of a population consist of lawyers and engineers, respectively, you would form the base rate fallacy that someone who enjoys physics in school would probably be categorized as an engineer rather than a lawyer. The baserate fallacy and its implications for the difficulty of intrusion detection.
Four common statistical misconceptions you should avoid. Indeed, a true attack always occurs extremely rarely. The tendency to ignore info about general principles in favor of very specific but vivid info. Section 5 then continues with an application of the baserate fallacy to the intrusion detection problem, given a set of reasonable assumptions. I have already explained why nsastyle wholesale surveillance datamining systems are useless for finding terrorists. The base rate fallacy, also called base rate neglect or base rate bias, is a fallacy. The major challenge for ids is the base rate fallacy. This article demonstrates that, for a reasonable set of assumptions, the false alarm rate is. Patrick florer the base rate fallacy information security. Heres a more formal explanation floyd rudmin, a professor at a norwegian university, applies the mathematics of conditional probability, known as bayes theorem, to demonstrate that the. An important requirement is that an intrusion detection system be effective. Any intrusion activity or violation is typically reported either to an administrator or collected centrally using a security information and event management siem system.
If the base rate is known, then a fourfold table, also called a 2 x 2 table or matrix, is a mechanism that helps us understand the correct. Base rate fallacy defined over half of car accidents occur within five miles of home, according to a report by progressive insurance in 2002. An intrusion detection system generates 1,000,100 log entries. Another mental trick i use for explaining the base rate fallacy is to suggest a screening system which always gives the more likely answer.
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