Eavesdropping, fraud, and message interception are crimes as old as communication itself. Everything but the information contained in our brains is accessible to other people, and not all those people have your best intentions in mind.

Intercepting and altering communication has happened for centuries, and the advent of the internet made it easier than ever for criminals to inject their interests into private transmissions. These nefarious acts are called man-in-the-middle (MITM) attacks. This type of cybercrime is common, potent, and devastating. (Note: This article about man-in-the-middle (MITM) attacks is also available as a free PDF download.)

Here’s what you need to know about MITM attacks, including how to defend yourself and your organization against them.

SEE: Cybersecurity strategy research: Common tactics, issues with implementation, and effectiveness (Tech Pro Research)

What are man-in-the-middle attacks?

The concept behind a man-in-the-middle attack is simple: Intercept traffic coming from one computer and send it to the original recipient without them knowing someone has read, and potentially altered, their traffic.

MITM attacks give their perpetrator the ability to do things like insert their own cryptocurrency wallet to steal funds, redirect a browser to a malicious website, or passively steal information to be used in later cybercrimes.

Any time a third party intercepts internet traffic, it can be called a MITM attack, and without proper authentication it’s incredibly easy for an attacker to do. Public Wi-Fi networks, for example, are a common source of MITM attacks because neither the router nor a connected computer verifies its identity.

In the case of a public Wi-Fi attack, an attacker would need to be nearby and on the same network, or alternatively have placed a computer on the network capable of sniffing out traffic. Not all MITM attacks require an attacker to have physical proximity to their victim, though–plenty of strains of malware exist that can hijack traffic and inject malicious information wherever an infection spreads.

SEE: All of TechRepublic’s cheat sheets and smart person’s guides

Combatting MITM attacks requires using some form of endpoint authentication, such as TLS or SSL, that uses an authentication key that ideally can’t be spoofed. Authentication methods have become stronger, leading to end-to-end encryption of some systems.

Two-factor authentication methods are one example of enhanced security against MITM attacks. Passwords are increasingly unreliable as a way to secure accounts and systems, and by adding a second factor like a hardware key, a software code, or other factor input separately, it becomes harder for attackers to intercept traffic or break encryption. That doesn’t mean encryption cracking doesn’t happen–hackers often manage to fake certificates and pose as banking websites, login portals, and other sites, which they use to steal information.

MITM attacks are the perfect example of the cybersecurity arms race: As soon as a new form of encryption is broken, organizations come up with a new one, which is in turn broken, repeating the cycle.

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What are famous examples of man-in-the-middle attacks?

There have been a number of well-known MITM attacks since the advent of the internet, but to paint a picture of just how widespread and powerful MITM attacks are it’s important to look back in history to one of the most powerful, which happened well before the invention of the computer: The Babington Plot.

In 1568, supporters of the imprisoned Mary, Queen of Scots, wrote her a letter asking her to support an assassination attempt on Queen Elizabeth I. Mary’s reply was intercepted by Elizabeth’s agents, who altered the letter to ask for the identities of the conspirators. The conspirators’ reply, complete with a list of names, was again intercepted by the men in the middle, leading to the execution of Mary and her co-conspirators.

SEE:A winning strategy for cybersecurity (ZDNet special report) | Download the report as a PDF (TechRepublic)

There are plenty of examples of internet-based MITM attacks as well.

  • The US National Security Agency posing as Google was revealed in 2013 when Edward Snowden leaked NSA documents to the public. Using its ability to intercept traffic and spoof SSL certificates, the NSA was able to keep tabs on potentially anyone’s Google searches.
  • Comcast was caught injecting JavaScript into its web traffic to show its own advertisements in place of those hosted by third-party sites.
  • Superfish, an adware program, was found to be scanning SSL traffic and installing certificates that allowed it to intercept and redirect secure traffic.
  • A major flaw in banking apps on Android smartphones opened up dozens of apps to MITM attacks.

There are many more examples to pull from, and likely even more attacks that go by unnoticed, but it all comes back to one thing: MITM attacks happen, and will keep being attempted for as long as there is an internet.

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Who is the typical target of a man-in-the-middle attack?

Any person or any organization could be the target of a MITM attack, but most of these crimes have a common theme: Financial gain. Banks and banking apps are popular targets for malware-based MITM attacks, as malicious code can wait until it detects traffic to a target site to steal packets, hijack traffic, or otherwise compromise secure connections.

That doesn’t mean only finance-related connections are popular targets: Any secure connection that could be compromised for private gain could motivate an attacker. This includes social media accounts, ecommerce site credentials, confidential databases, and others.

The Internet of Things (IoT) is becoming an increasingly popular target for MITM attacks because of rapid growth of IoT devices has outpaced security. IoT devices also have the potential to deliver a large amount of personally identifying information about individuals and businesses, making hijacking their traffic an appealing prospect for cybercriminals.

SEE: Enterprise IoT research: Uses, strategy, and security (Tech Pro Research)

Businesses that operate Industrial Internet of Things (IIoT) hardware are at particular risk for MITM attacks because of lax security practices and sensitive proprietary information that IIoT machines have access to. MITM attacks on IIoT systems could cause business downtime, manipulate products to make them weaker or less secure, and steal proprietary information that IIoT machines use in manufacturing.

In short, everyone transmitting sensitive information over the internet is a potential MITM target, though business attacks that could financially benefit hackers or give competitors an edge are a larger threat due to the sheer volume of damage they could do.

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What are the types of man-in-the-middle attacks?

Protecting your computers from MITM attacks, whether at home, on the road, or in the office, depends on knowing what you’re protecting yourself from. MITM attacks take different forms, target multiple vulnerabilities, and come from a variety of sources. Staying safe requires knowing what kinds of MITM attacks are possible and how to protect against all of them.

SEE: Incident response policy (Tech Pro Research)

These are the various types of man-in-the-middle attacks.

  • Rogue access points are set up to trick computers that automatically connect to Wi-Fi by posing as legitimate public networks. These rogue networks often monitor traffic and steal sensitive information.
  • Address resolution spoofing involves a malicious node on a local area network posing as another machine to trick a victim into connecting to it before passing traffic on to the legitimate node.
  • mDNS spoofing fools network devices into connecting to fake addresses. mDNS is used to match names to addresses on local area networks, and when spoofed give malicious machines access to vulnerable computers and IoT hardware.
  • DNS spoofing is commonly used to trick internet users into connecting to fake websites set up to look like real ones. This method is common in online banking fraud and other account hijacking attacks.

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How do I prevent man-in-the-middle attacks?

Protecting yourself against these various forms of MITM attacks requires several steps, and each is essential at stopping a particular form of attack.

  • Don’t allow computers or mobile devices to connect to Wi-Fi networks automatically–make sure you’re only connecting to known, trusted Wi-Fi networks.
  • Make sure all access points you control are secured and encrypted. Attackers that rely on physical proximity to deploy MITM attacks can be kept off a network by good security.
  • If you are connecting to an unknown or public Wi-Fi network, be sure to use a VPN to secure your traffic.
  • Never share sensitive information with a website that doesn’t use secured HTTP, indicated by a URL that begins with https://.
  • Add a second authentication factor to any accounts that allow it.
  • Keep an eye out for phishing attempts, or any email that requests you click on a link to log in to a website. If you’re unsure of the legitimacy of an email, navigate to the website in question manually and log in without using the email link. If you are still unsure, contact the organization that operates the site to see if it is a legitimate message.
  • Make sure operating systems are updated to prevent MITM attacks that exploit system weaknesses.
  • Install an up-to-date antivirus application, and be sure it is set to scan your computer on a regular basis.

You’re never completely secure from a MITM attack or any other kind of cybercrime, but by being vigilant you can greatly reduce your risks and ensure that you’re too tough of a target to waste time on.

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Image: utah778, Getty Images/iStockphoto

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Strengthen your organization's IT security defenses by keeping abreast of the latest cybersecurity news, solutions, and best practices. Delivered every Monday, Tuesday and Thursday