Don't Open Attachments You Weren't Expecting — Even From People You Know

One of the oldest tricks in digital attacks is sending malicious files from compromised accounts. Your friend's email gets hacked, and suddenly you get an invoice or a "check this out" attachment from someone you trust. The instinct to open it is strong precisely because you recognize the sender.

Make it a rule: if you were not expecting a file, verify before opening. A quick message — "Hey, did you just send me something?" — takes ten seconds and can prevent weeks of damage. This applies to links too, not just attachments.