What is false positive and true positive in cyber security?

    Glossary

False Positive

Definition(s):

  An alert that incorrectly indicates that a vulnerability is present.
Source(s):
NIST SP 800-115

  An alert that incorrectly indicates that malicious activity is occurring.
Source(s):
NIST SP 800-61 Rev. 2

  An instance in which a security tool incorrectly classifies benign content as malicious.
Source(s):
NIST SP 800-83 Rev. 1

  Incorrectly classifying benign activity as malicious.
Source(s):
NIST SP 800-86

  An erroneous acceptance of the hypothesis that a statistically significant event has been observed. This is also referred to as a type 1 error. When “health-testing” the components of a device, it often refers to a declaration that a component has malfunctioned – based on some statistical test(s) – despite the fact that the component was actually working correctly.
Source(s):
NIST SP 800-90B under False positive

confusion matrix is a table that is often used to describe the performance of a classification model (or “classifier”) on a set of test data for which the true values are known. In simple words, we use a confusion matrix to compare the accuracy of the predicted value of the classification model with the actual value of the dataset.

We have four sections in the confusion matrix:-

a) True Negatives (TN): It means the predicted value is negative which is the same as the actual value.

b) False Positive (FP): It means the predicted value is positive but the actual value is negative.

c) False Negatives (FN): It means the predicted value is negative but the actual value is positive.

d) True Positives (TP): It means the predicted value is positive which is the same as the actual value.

Many cybercrimes can take place by the two types of error in the confusion matrix :

  1. Type I Error (FP)
  2. Type II Error (FN)

There are four possible states in Intrusion Detection Systems (IDS) for each activity observed. A true positive state is when the IDS identifies an activity as an attack and the activity is actually an attack. A true positive is a successful identification of an attack. A true negative state is similar. This is when the IDS identifies an activity as acceptable behavior and the activity is actually acceptable. A true negative is successfully ignoring acceptable behavior. Neither of these states is harmful as the IDS is performing as expected. A false positive state is when the IDS identifies an activity as an attack but the activity is acceptable behavior. A false positive is a false alarm. A false negative state is the most serious and dangerous state. This is when the IDS identifies an activity as acceptable when the activity is actually an attack. That is, a false negative is when the IDS fails to catch an attack. This is the most dangerous state since the security professional has no idea that an attack took place. False positives, on the other hand, are an inconvenience at best and can cause significant issues. However, with the right amount of overhead, false positives can be successfully adjudicated; false negatives cannot.

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In this section, we'll define the primary building blocks of the metrics we'll use to evaluate classification models. But first, a fable:

An Aesop's Fable: The Boy Who Cried Wolf (compressed)

A shepherd boy gets bored tending the town's flock. To have some fun, he cries out, "Wolf!" even though no wolf is in sight. The villagers run to protect the flock, but then get really mad when they realize the boy was playing a joke on them.

[Iterate previous paragraph N times.]

One night, the shepherd boy sees a real wolf approaching the flock and calls out, "Wolf!" The villagers refuse to be fooled again and stay in their houses. The hungry wolf turns the flock into lamb chops. The town goes hungry. Panic ensues.

Let's make the following definitions:

  • "Wolf" is a positive class.
  • "No wolf" is a negative class.

We can summarize our "wolf-prediction" model using a 2x2 confusion matrix that depicts all four possible outcomes:

True Positive (TP):
  • Reality: A wolf threatened.
  • Shepherd said: "Wolf."
  • Outcome: Shepherd is a hero.
False Positive (FP):
  • Reality: No wolf threatened.
  • Shepherd said: "Wolf."
  • Outcome: Villagers are angry at shepherd for waking them up.
False Negative (FN):
  • Reality: A wolf threatened.
  • Shepherd said: "No wolf."
  • Outcome: The wolf ate all the sheep.
True Negative (TN):
  • Reality: No wolf threatened.
  • Shepherd said: "No wolf."
  • Outcome: Everyone is fine.

A true positive is an outcome where the model correctly predicts the positive class. Similarly, a true negative is an outcome where the model correctly predicts the negative class.

A false positive is an outcome where the model incorrectly predicts the positive class. And a false negative is an outcome where the model incorrectly predicts the negative class.

In the following sections, we'll look at how to evaluate classification models using metrics derived from these four outcomes.

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Last updated 2022-07-18 UTC.

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What is false positive in cyber security?

An alert that incorrectly indicates that a vulnerability is present.

What is true positive and false positive example?

In this example, there are two classes of fruits. We had 9 apples and 10 strawberries, but the model identified only 6 apples (true positive) and 8 strawberries (true negative) correctly, moreover, the model predicted 2 strawberries as apple (false positive) and 3 apples (false negative) as strawberries.

What is false positive and false negative in security?

A false positive state is when the IDS identifies an activity as an attack but the activity is acceptable behavior. A false positive is a false alarm. A false negative state is the most serious and dangerous state. This is when the IDS identifies an activity as acceptable when the activity is actually an attack.

What is a false positive examples?

Some examples of false positives: A pregnancy test is positive, when in fact you aren't pregnant. A cancer screening test comes back positive, but you don't have the disease. A prenatal test comes back positive for Down's Syndrome, when your fetus does not have the disorder(1).