What are common email-based malware types (Trojans, ransomware, worms)?

You open what looks like a shipping confirmation from a courier you actually use. The attachment seems normal. You click it. That's often all it takes.

Email is the most common delivery vehicle for malware, and the three types you'll see most often are Trojans, ransomware, and worms. Each works differently, but they all rely on the same basic trick: making you think the email is legitimate.

Trojans are the most common. They disguise themselves as something harmless, an invoice, a shipping notice, a document you were supposedly expecting. Once you open the file and run it, the Trojan quietly installs itself and opens a backdoor. The attacker can then access your system remotely, often without any obvious signs that something is wrong. You might not notice for days or weeks.

Ransomware is the one that makes headlines. It arrives the same way (a malicious attachment or a link to a poisoned download), but once it runs, it encrypts your files and locks you out. Then comes the demand for payment to get them back. For businesses, a ransomware attack can mean days of downtime, data loss, and real financial damage. The email that delivers it often looks completely routine.

Worms are a bit different. Once a worm gets onto a device, it spreads automatically by emailing itself to everyone in your contacts. No further action from the attacker needed. Worms are less common than they used to be, partly because modern email filters catch many of them, but they still cause problems inside organisations where internal email traffic gets less scrutiny than inbound mail from outside.

From a deliverability angle, this matters more than you might think. If a domain or IP gets associated with malware delivery (even accidentally, through a compromised sending account), it can end up on a blocklist fast. Proper email authentication with SPF, DKIM, and DMARC won't stop malware, but it does prevent attackers from spoofing your domain to deliver it. That protects your reputation as well as your recipients.

If you want to understand what actually gets caught before it reaches the inbox, the next question covers how malicious attachments work and what filters look for.