Title image remixed from an original by Konstantin Maslak (Shutterstock).
Stupid Thing #1: You Undervalue Your Personal Data
Fortunately, you can have your cake and eat it too. If you don't like targeted ads based on your search history, you can just utilize your browser's Do Not Track options (read this to learn how to enable them). Facebook now offers lots of ways to set the level of privacy you want to maintain, which is great, but with all the options it can be tough to learn and get just the way you want. Our always up-to-date guide to managing your Facebook privacy can get you up to speed. One of the first things you should do with Facebook is prevent apps from using your personal data as much as possible. Signing up for an app can provide the developers with much more information than you may realize as the apps will take information they don't necessarily need. To find out what each app is doing and limit its reach, just click the downward-facing triangle in the upper-right hand corner of your Facebook page and choose "Account Settings." From there click the Apps tab and click the "Edit" link next to any app. You'll see a list of what it is allowed to do plus the information it can access. Some stuff will be required for the app to function, but you'll almost always find something that isn't. Click the "Remove" link to revoke the app's permission to access that information.
Stupid Thing #2: You Submit Sensitive Information Over an Insecure Connection
This isn't a big deal if you're just reading or watching something, but if you don't see https:// you should avoid sending sensitive information like your credit card number or address. If you'd like to know more about HTTPS, read our guide. Also, the insecurity of HTTP isn't as big of a deal when you're on your password-protected home network, but when you're on a public Wi-Fi connection, anyone can snoop on what you're doing.
Stupid Thing #3: You Feed the Trolls
First, it's important to remember that trolls are not attacking you—they're attacking boredom. They have nothing better to do than say something mean so that's how they've unfortunately chosen to spend their time. If what they're saying isn't going to have much of an impact on anyone, just remember that they're bored, loathsome people and let it go. On the other hand, if they're promoting hate speech and potentially causing harm to others, it's best to avoid engaging them and instead report them to the site's administrator. Many sites offer a means of flagging harmful posts, and commenting systems offer ways for an administrator to ban problematic users. A simple email is often sufficient to take care of a bad person. Engaging with a troll-ish thread is just going to make you angry and potentially get you in trouble, too. If you do fall into the trap of feeding a troll, however, using the principles of cognitive therapy can be a worthy solution. This means responding positively and calmly, while accepting their different opinion. The trolls will likely find it frustrating and even condescending, but it's hard to argue with someone who is accepting your point of view (or even agreeing with you).
For more tips on de-trolling your internet, read this.
Stupid Thing #4: You Leave Private Information in Your Web Browser
Keeping your browser activity private can be a lot of work, but there are a couple of things you can do to take the pain out of it. First of all, if you're doing anything particularly private on your computer you can just log out or lock people out with a password. Enabling a guest account can be very useful so when anyone wants to use your computer they won't be entrenched in your embarrassing web activity. If you don't want to password-protect anything, the next best thing you can do is just quit your browser whenever you're done using it and set it to clear your history when you do. On top of that, make sure you log yourself out of any accounts or your browser handles that for you. For the super paranoid, clear your cookies as well. One of our favorite tools for the job is CCleaner (the first 'C' stands for Crap), available for Windows and Mac.
CCleaner will give you a good start, but the fact of the matter is that a determined snoop has a ton of ways to spy on your browsing behavior. To subvert even the most clever snoop, check out our guide to really browsing the web without leaving a trace. For more tips and tricks, read how to protect your privacy when others have access to your computer.
Stupid Thing #5: You Don't Keep a Backup of Online Data
Some data, like photos and videos, can simply remain backed up on a local hard drive. If you lose your content online, you can always access a local copy and upload it elsewhere. That's all well and good if you create your content locally on your computer, but there is plenty you create online as well and that data is only saved on the server. In the case of Facebook, you can simply download all of your data in one big chunk. All you have to do is go into your account settings and look for the "Download a copy of your Facebook data" link at the bottom of the page. Not all web apps allow a full data download like Facebook, however, and you'll need to employ other services. InSync will handle your Google Docs. Backupify can back up multiple web services like Google Apps, Twitter, Facebook, and more. If you keep any vital data online, be sure you use something to back it up. If you don't, it could be gone tomorrow with no way to get it back.
Stupid Thing #6: Assuming Your Posts and Comments Are Anonymous
It's not that it's impossible to comment anonymously online—and we've offered some tips for doing just that—but most of us don't follow a strict enough set of rules to remain anonymous. Even if you don't use your real name, comments stick. You'll probably use that pseudonym down the line and it will gain its own reputation. Your name may be tied to that pseudonym on as little as one web site and people will be able to find out who you are with a simple search. Additionally, you may post a comment on a blog or other page without realizing that you're already logged in via your Facebook account. There are a lot of ways your name can be tied to what you say online, so it's important to remember that your reputation is riding on every post to some extent. Remember to think about what you're going to say before you say it or it may follow you around for much longer than you expect.
Stupid Thing #7: You Let People Track Your Whereabouts
Stupid Thing #8: You Use an Insecure Password That You Rarely (or Never) Change
Your professor says an awful lot of things during class. You can't possibly write it all down, nor should you. To take the best notes (and ace your exams), pay attention to your professor's cues—conscious and subconscious. 