Recognizing Computer Threats: Email

By Chris Williams

Promotional email

Chances are, if you see an unsolicited email that appears to originate from a company that you don’t recall signing up for, it’s probably spam or phishing. Since many retailers require double opt-ins now, it’s more difficult to get “accidentally” registered for an email subscription than it was a decade ago. Regardless, we recommend doing a follow-up with the company in question just to be sure; our goal is to rule out the possibility that your email account was hacked (see previous posts on compromised email accounts for a primer on this topic).

When dealing with a potential phishing email do not use the URL, email address, or phone number provided within the suspicious communication; instead look up the company’s information via your preferred search engine, making sure you are on the company’s direct website (not a competitor, affiliate, or knock-off). If the message is a scam the contact info provided won’t usually point to the real entity—it will more likely take you to a fake site that will attempt to capture your credentials or trick you into installing malware.

Scenario: fake offer with malicious “unsubscribe” link

Tom signs into his Gmail account and reads the contents of his inbox. He sees a bunch of ads for games and T-shirts he’d like to have, along with an advertisement from a company he doesn’t remember doing business with: “”. Maybe someone registered his email address on their mailing list due to a typo? No problem: Tom simply clicks the Unsubscribe link down at the bottom of the email message, expecting it to take him to a website where he can manage his “subscription”; only one problem, the email was actually a phishing scam, and the moment his browser navigated to the malicious URL (disguised as the Unsubscribe link, of course) it started a drive-by-download which infected his system with malware. Antivirus warnings start flashing and the threat is neutralized—or is it?

What could Tom have done differently? For starters, he could have done a Google search on this company to make sure it’s even real. Sometimes phishing emails are convincing, sophisticated messages with official-looking logos (stolen from PayPal, Amazon, etc.); sometimes they are terrible hacks with bad grammar and poor punctuation. In the latter case, the companies being represented may or may not even exist.

Let’s discuss our hypothetical in a bit more detail:

If came up as a search result via a reliable search engine such as Google, at least Tom would know that the company isn’t totally fictitious. However, that doesn’t mean the communication itself is legit, so we must dig a bit deeper.

Both the web address and phone number for should be published online. Tom can simply navigate to their site (again, using a reliable search engine to locate it) and find whatever contact info he needs to verify his “subscription”. He can call, email, or see if they offer a way to manage email opt-outs directly on the site.

Let’s assume there is no email address or subscription management feature on the site. No problem! A phone call to customer service will suffice. We expect one of two scenarios to occur:

  • Tom calls and speaks to an agent, provides his information, and is told that his email address is not on file with


  • Tom calls and speaks to an agent, provides his information, and learns that he was in fact signed up for promo emails. He then unsubscribes, assuming at this point that it was due to a mistake (maybe his address is similar to another user’s—it’s pretty commonplace for that to occur).

Malicious attachments

“What if there’s no URL in the body of the message? Perhaps the email just has a harmless little .zip file attached… no way that can be bad, right?”

Malicious attachments are one of the most insidious vectors used to infect victims with malware; within this category of threat, there are perhaps two major methodologies in widespread use: disguising the attachment’s file extension, and hiding the payload inside “real” data. An example of the former would be a malicious file masquerading as a .pdf file or Word document; an example of the latter would be a Macro-enabled Excel workbook that runs a malicious script when opened.

Fortunately, many email filtering systems can be configured to block any attachments with mismatched file extensions (the file extension shown in the document name doesn’t match its actual file type), and most systems can simply blacklist certain “high-risk” file extensions altogether. For instance, files with .zip extensions are often blocked entirely by anti-spam platforms; this is because they are so prevalent in phishing campaigns and very effective. As long as the file containing the payload is still zipped it will typically appear clean to antivirus software. While there may be a window of time to scan the file and prevent infection, this isn’t always the case.

The takeaway

Spam and phishing emails are increasing in frequency and complexity as scammers become savvier. Unfortunately, a contributing factor in this increase is the fact that these scams successfully fool a lot of people; users that open links and attachments they should have avoided are a major vector for the spread of malware. Similarly, unsuspecting users can be led to bogus versions of real sites and voluntarily give up their personal and account info.

Some file extensions are more suspect than others, but all attached files should be treated as suspect unless you have reasonable assurances of their legitimacy.

For the sake of repetition: never click a link provided in an email message if you aren’t sure of the authenticity of the message and/or its sender. Contact the company using a known-good phone number or email address.

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