The internet is great, but it's complex and it can be easy to make some dumb mistakes even when you're smart enough to catch them most of the time. We want to know what common but mistakes you've made, have seen others make or worry about making.
The title photo, which was too weird not to use, was created by Voronin76 (Shutterstock).
Chances are most of the stupid things we all do online pertain to privacy and security issues, but they don't have to. Maybe you fell for a phishing scam or fed a troll. Perhaps there's just something a lot of people do online that seems pretty stupid to you. Please share your dumb online mistakes -- or the mistakes of others you know -- in the comments. But let's not let things get too negative or hostile, and rather focus on common online mistakes we all can be prone to make and have possible solutions.