Is Windows Defender enough or do you still need antivirus?

Do I need antivirus if I have Windows Defender? Most people assume that the built‑in Windows Defender covers every threat, and they’re often right for day‑to‑day web browsing. The mistake is thinking it’s a set‑and‑forget solution for every environment. We saw this this week when a local accountant brought in a laptop that had been running fine for months. The fan was screaming, CPU at 100% in Task Manager, and the machine kept crashing every time a client spreadsheet opened. The client panicked, fearing a ransomware hit that could lose a morning’s worth of work. Our first step was to check Windows Security. Defender was active, but its real‑time protection had been disabled by a rogue browser extension that the user had installed to block ads. The extension also had opened a back‑door for a low‑level trojan that was silently mining cryptocurrency, explaining the heat and the slowdown. What does Windows Defender actually protect against? Defender provides three core layers: Signature‑based malware detection – it recognises known viruses and ransomware. Behavioural monitoring – it can spot suspicious actions like a programme trying to encrypt many files. Cloud‑based reputation checks – it queries Microsoft’s servers for the latest threat intel. For a typical home user who sticks to reputable sites and keeps Windows updated, this is often sufficient. However, Defender does not scan every third‑party installer as aggressively as many paid solutions, and it can be fooled by socia