email viruses explained

An email virus is a malicious code or a link to malicious code sent via email. The virus can replicate itself, quickly spreading from one device to another. Most users on the internet are familiar with email viruses and the unpleasant consequences they can have on personal devices.

The question is, “Are you aware of an infection's serious implications for your company?” An email virus can not only infect the victim's computer but also infect the computers of those sharing the same network.

Email viruses are incredibly prevalent and can compromise sensitive information, destroy data, harm hardware, and waste time, resources, and energy. Three hundred thousand new pieces of malware are created daily, including viruses, adware, Trojans, keyloggers, etc., to steal data.

Watch: Best Practices to Avoid Email Virus Infections

What are Email Viruses and How Do They Work?

Email viruses, which constitute the majority of computer viruses, consist of malicious code that is distributed in email messages, and can be activated when a user clicks on a link in an email message, downloads an email attachment, or interacts in some other way with the body of an infected email.

Virus emails are usually programmed to be sent to everyone in the victim's address book once their computer has been infected and tend to increase quickly. There are three primary ways an email virus can infect a victim's email and computer; phishing email, included in an attachment, or embedded within the email body.

Email viruses often look like executable files with extensions such as the following:

  • .exe
  • .dll
  • .com
  • .bat
  • .cmd
  • .pif
  • .scr
  • .dot
  • .xls
  • .xlt
  • .docm
  • .pdf

How Is an Email Virus Delivered?

Close up of businessman hand holding tablet with abstract glowing keyhole padlock interface on blurry background. Protection, safety and technology concept. Double exposureViruses are commonly linked to phishing attacks, in which threat actors send out fraudulent emails from spoofed or compromised accounts that appear to have been sent from authorized sources to trick users into sharing sensitive information. These attacks often leverage stealthy social engineering techniques to manipulate psychology and deceive victims. Spam, ransomware, business email compromise (BEC), whaling, and ransomware are among other attacks that are notorious for infecting systems and compromising networks with email viruses. Viruses can be included as an attachment in a malicious email or in the body of the email itself. 

Some viruses capitalize on nothing but user naivety. Have you ever forwarded a chain letter, a virus warning, or a desperate plea for help? If so, you probably fell for a hoax and helped to spread a virus. In these scenarios, the virus is the email itself. Collectively, these emails clog up mail servers and inboxes and frequently deny service to legitimate users while the system processes these bulk messages.

Types of Email Viruses

There are many forms of email viruses, and new zero-day viruses are rapidly emerging, making securing email in this modern digital threat environment even more complex. Some types of email viruses are more dangerous than others. A few of the most threatening types of email viruses include:

  • Boot sector viruses: This type of virus is one of the most dangerous types for most users. These viruses spread on the master boot record, making them difficult to remove and frequently resulting in a complete system reformat.
  • Direct action viruses: This type of virus is one of the two main types that infect files. These viruses work through files they attach to rather than hiding in a computer’s memory or installing themselves. The attached virus is activated and spreads when a user clicks on an infected file. Although direct-action viruses make files inaccessible, they don’t affect a system’s performance.
  • Resident viruses: Like direct action viruses, resident viruses infect files. However, this type of virus installs itself on a PC. These viruses are hazardous because they can persist even after the primary source of the virus is removed.
  • Multipartite viruses: This type of virus can spread in various ways and behave differently depending on factors such as a PC’s operating system. These viruses can infect the boot sector and files on a computer, spread rapidly, and be difficult to remove.
  • Keyloggers: A keylogger is a type of spyware that, when installed on a device, enables a malicious actor to track and log the keys that the user strikes on their keyboard, capturing information that is typed, such as personal and financial data, PIN codes and account numbers, credit card numbers, usernames, passwords, and other sensitive data without the user's knowledge. This information can be used to commit fraud or identity theft.
  • Polymorphic viruses: This type of virus changes its signature when it reproduces, masquerading as a different and seemingly harmless file. These viruses are especially threatening because antivirus programs have difficulty detecting them. Because traditional antivirus software can only blocklist a single virus variant, many programs take months to identify a single polymorphic virus.

Polymorphic Viruses and Pattern Avoidance

Polymorphic viruses have code that changes how they operate, thus defeating detection by standard methods. These complex and hazardous viruses employ various tactics to modify themselves during each infection. They vary their physical file makeup by encrypting their codes and using different encryption keys generated by mutation engines each time they infect a device. This technique allows most polymorphic viruses to remain undetected by antivirus software engineered to recognize a static, unchanging code.

Polymorphic viruses are usually spread via spam email, malware, or infected websites. VIRLOCK, one of the most notorious polymorphic viruses, evolved to combine file infection and ransomware, making it especially difficult to detect and remove.

How are Email Viruses Detected?

Close up of businessman hand holding tablet with abstract glowing keyhole padlock interface on blurry background. Protection, safety and technology concept. Double exposureAs computer viruses have become increasingly problematic, detection methods have evolved to combat them. There are several different methods that antivirus programs employ to identify viruses, malware, and other computer threats. These methods include:

  • Signature-based detection: Traditional antivirus software relies heavily on signature-based detection to identify viruses and malware. In this method, each time a new malware variant is discovered and arrives in the hands of an antivirus company, a signature of the file is extracted and added to the signatures database of the antivirus software. This approach has limitations, as threat actors have tried to outsmart signature-based antivirus software by creating advanced viruses that modify themselves as a method of disguise to avoid matching existing virus signatures.
  • Heuristics: Heuristic analysis is a popular and effective method for detecting previously unknown viruses and new variants of viruses already in the wild by examining code for suspicious properties. This technique determines the susceptibility of a system to a particular threat using various weighing methods or decision rules. Heuristics analysis is one of the few methods capable of identifying polymorphic viruses.
  • Real-time protection refers to the automatic protection provided by many antivirus and anti-malware programs, which monitor systems for suspicious activity.
  • Sandbox detection: This behavior-based detection technique runs programs in a virtual environment, logging programs’ actions and behaviors. Depending on the actions logged, antivirus engines that utilize this technique can determine whether a program is malicious or not. This technique has proven highly effective but is rarely used in end-user antivirus solutions due to its slowness.
  • Data mining techniques: In this relatively new approach to virus and malware detection, data mining and machine learning algorithms are used to classify the behavior of a file and determine whether it is malicious or benign depending on a series of features extracted from the file.

Regardless of the techniques that it utilizes to detect viruses and other threats, antivirus software has its limitations. For instance, antivirus programs are often ineffective in detecting zero-day viruses. Even those that use non-signature-based methods frequently need to catch up. Virus designers test the new viruses they create on established antivirus applications to ensure they are not detected before releasing these viruses into the wild.

Best Practices for Recognizing Email Viruses & Preventing Infections

Knowing how to recognize an email virus and implementing basic email security best practices is imperative in protecting yourself and your company from infection. Here are some tips for identifying viruses and preventing infection:

  • Refrain from clicking through links embedded in email messages.
  • Avoid opening potentially dangerous email attachments included in emails from unknown senders.
  • Scan all attachments for malware.
  • Watch for phishing emails, and know what to do if you click on a phishing link.
  • Keep your mail client, operating system, and web browser updated and patched.
  • Do not open any executable files included as email attachments - attackers often name these files with two extensions to disguise them.
  • Ensure that your mail program is set not automatically to download and open attachments or display HTML content.
  • Verify the source of any suspicious email that you receive.
  • Avoid forwarding emails unless you have verified that they are legitimate. 
  • Be cautious when sharing your email address - if it gets into the wrong hands, it can be used to send a convincing email containing a virus. 
  • Get a text preview in your email service - content previews give you a glance at the content in an email without having to click on the email.
  • Close pop-up ads by right-clicking on them in your taskbar - not by clicking the “X” in the corner 
  • Implement a comprehensive, fully-managed cloud email security solution that provides complete end-to-end control of your email.
  • Always remember: act smart, not fast!

How to Protect Against Email Viruses

Antivirus software plays a vital role in protecting against email viruses; however, this technology must be implemented as an element of a comprehensive, multi-layered cloud email security solution to combat advanced attacks effectively.

Defense in depth is imperative to a successful email security approach. No security feature or antivirus software can protect against today’s sophisticated email threats like ransomware, spear phishing, and zero-day attacks. Look for a cloud email security solution composed of multiple layers of protection that work harmoniously to detect and block advanced and emerging threats in real time, preventing the potential harm and tremendous inconvenience that can result from email viruses or other malicious threats.

How Guardian Digital Can Help

Guardian Digital EnGarde Cloud Email Security provides comprehensive protection against viruses, malware, spam email, and other dangerous attacks that daily threaten email users. Benefits of choosing EnGarde to secure your business email include:

  • Multi-layered architecture, where individual layers of security work in concert to provide complete, resilient protection
  • Fully-managed, end-to-end control of your email, preventing malicious messages from reaching the inbox
  • Adaptive antivirus engines and advanced heuristics technologies can detect the most advanced polymorphic viruses and malware variants.
  • Secure endpoint encryption using strong cryptography
  • Tighter security, flexible implementation, and eliminated risk of vendor lock-in through the use of a transparent, collaborative development approach
  • Centrally managed cloud-based administration
  • Exceptional 24x7x365 customer support, conveniently providing you with the peace of mind to focus on aspects of running your business besides email security

Keep Learning About Virus and Threat Protection

In the modern digital landscape, threats are everywhere, and cybercriminals continuously seek ways to deploy their malicious tactics. Because of this, taking as many preventive measures as possible is of the utmost importance. Remember, the prevention of an attack is far better than mitigation.

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