How to Protect Against the Dangers of Malicious Email Attachments

Lauryn Cash
Written by Lauryn Cash
News and Commentary /
How to Protect Against the Dangers of Malicious Email Attachments

More than 300 billion emails are sent every day. And while the vast majority are harmless, an ever-growing number contain malicious email attachments.

Email attachments we send, such as PDFs, image files, or spreadsheets, are the perfect hiding place for various scams and attacks. Unfortunately, what seems like a simple file attachment can turn out to be a destructive virus or a sophisticated piece of ransomware—and opening it can harm you and cost your organization.

As the number of cyberattacks rise, the danger of ill-intentioned attachments increase. However, you can still protect yourself from malicious email attachments by knowing what to look for and implementing proper cybersecurity measures.

Types of Malicious Email Attachments

The term malicious email attachment refers to a class of email-based attacks. There are several types of cyberattacks that malicious actors can deliver via simple email attachments. Let’s briefly look at some common ones.


Malware, or malicious software, can be delivered via email as an attachment. You may be familiar with certain types of malware, such as:

  • Trojans
  • Worms
  • Spyware
  • Adware

At best, malware can be irritating or distracting; at worst, it can cripple your device and siphon sensitive information.


Technically a type of malware, ransomware holds your device hostage until the cybercriminal receives payment which is usually, but not always, a sum of money.

Once you accidentally download ransomware onto your device, the software uses encryption to block access to part or all of the system. If you don't pay the ransom in time, your files may be leaked, deleted or sold on the dark web. Unfortunately, paying the ransom doesn't always restore access and could also harm your brand’s reputation in the process.


Viruses are another form of malware that can infect your device. Some computer viruses can lie dormant for days or weeks, waiting for the right action to trigger them. Computer viruses can replicate and spread throughout your device like real-world viruses.

A virus may:

  • Log keystrokes
  • Copy passwords
  • Corrupt system files
  • Send emails to your contacts

Spoofed Documents

Document or extension spoofing is a less sophisticated—but equally damaging—method of delivering a malicious email attachment.

When attackers “spoof” a document, they disguise their malicious attachment as something safe. There are various ways to spoof a document. A common tactic is to add a well-known extension type to the end of a file name.

How to Recognize Malicious Email Attachments

As the senders of malicious email attachments become increasingly clever, it can be challenging to spot one on your own. However, a handful of signs should alert you that something phishy is afoot.

Unusual File Extensions

Any file can include dangerous content, so don’t ignore file types seen in everyday business workflows. Per Trend Micro, the following file types should be filtered or blocked within emails:

Targeted Attacks

  • .doc
  • .jpeg
  • .pdf
  • .rtf
  • .xls
  • .zip

Malware Attacks

  • .doc
  • .exe
  • .xls
  • .rtf
  • .pdf
  • .scr
  • .vbs

Urgency in the Subject Line and Email Body

The business world is undeniably fast-paced. But when an email is littered with urgency terminology, there’s a decent chance the sender is after something more than a quick favor.

Why is urgency a red flag? Scammers and malicious actors use social engineering to create a sense of urgency, keeping you from second-guessing your actions or seeking advice from an expert.

Some of the terms to look out for include:

  • ASAP
  • Urgent
  • Today
  • Tomorrow
  • Next pay period
  • Right away

Of course, sometimes a request is urgent. Think about why the email is so time-sensitive. If the email was not expected, the best course of action is to confirm personally with the sender before complying with the request. Bottom line: trust your instincts.

Unknown Senders

“Stranger danger” is an essential mantra in email security. If you receive an attachment from someone you don’t know—especially if they’re from outside your organization—proceed with caution.

Ask yourself why the sender would reach out to you. If you can’t find a solid reason, you may want to leave that attachment unopened.

How to Protect Against Malicious Attachments

Because malicious files can damage your device and your organization, it’s essential to take steps to protect yourself from them. Here’s how to thwart would-be attackers.

Educate Users

Regardless of the size of your organization, it’s essential to teach your people how to spot suspicious attachments.

Aside from sharing the above tips on recognizing malicious email attachments with your team, you can advise them to:

  • Look out for emails with poor spelling and grammar
  • Leave unexpected attachments unopened
  • Refer to online learning centers
  • Keep software up to date
  • Inform the IT department of suspicious activities

Guard Against Malicious Email Attachments With Armorblox

Even with the best education, people can let their guard down, make mistakes, or fall victim to a never-before-seen type of email attack. The truth is that no amount of training will keep your organization 100% safe – business email compromise scams are constantly changing and becoming increasingly sophisticated and targeted; slipping past native email security layers.

With that in mind, email security solutions like Armorblox are the best way to protect your people and business from malicious email attachments. Armorblox warns users about potentially malicious attachments and automatically deletes or quarantines emails that appear harmful, as well as shielding you from:

By harnessing the powers of Machine Learning (ML) and Natural Language Understanding (NLU), Armorblox continuously learns how to keep you safe from all forms of Business Email Compromise (BEC). With a sophisticated security solution on your side, you can send and receive emails in complete confidence.

Take our interactive product tour to learn more about how Armorblox protects you, your business, and your data.

Take BEC Tour

Read This Next