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Windows Defender is decent for a basic level of protection, but relying on it alone is definitely risky. It can catch a decent amount of known threats - probably falls in that range people have been talking about - but there's a lot of newer malware, sophisticated ransomware, and those banking trojans that slip right past it. The thing is, Windows Defender mainly uses signatures of viruses that are already cataloged, so if you run into something really recent or customized, it might not recognize it.
The practical thing I haven't seen anyone mention here is using Windows Defender together with a complementary heuristic analysis tool, like Malwarebytes (which you run occasionally, you don't even have to leave it running 24/7 if you don't want to). Malwarebytes detects suspicious behavior in a different way than Defender, you know? It looks at patterns in how a program acts instead of just comparing against a database. You run it once a week or when something seems off, it takes 15-20 minutes, and it catches a lot of stuff that would slip past signature detection. It really helped me when I downloaded some weird files.
Beyond that, the real truth is no antivirus in 2026 is going to catch everything. You actually have to practice good browsing habits - don't open random attachments, be suspicious of links in emails, don't download from sketchy sites. Antivirus is your last line of defense, not your first.
I agree with what was said above. In my 26 years of experience, I've seen a lot of people relying too much on a single protection program and then getting a nasty surprise.
Windows Defender sits around 85-90% effectiveness in independent tests, which is reasonable for someone who doesn't want to spend anything, but the truth is new malware pops up constantly and no software can catch everything.
If you use your phone or computer for important stuff, like banking or sensitive photos, it's worth combining Defender with another more robust antivirus and, most importantly, having common sense: don't open strange attachments, don't download from suspicious websites, those basic things really.
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