Just a short, general list of things that everyone—amateurs to tech junkies—should keep in mind when using the Internet. Also, I want to make sure I don't go a whole month without posting again.
1) Don't believe everything you see—especially if it looks too good to be true.
This means something different for every Internet user. If you're a student, it means don't use Wikipedia as a source. If you're a consumer looking to buy something, it means don't trust the ads that pop up or assault you on every webpage you visit. Really, you should follow the same general rules that you (should) use in real life: don't blindly take anyone's word for anything, and if something looks too good (or too convenient) to be true, then it probably is.
2) Be careful with online commerce.
I would caution against paying for something online if you have alternatives. Increasingly, more and more companies are mandating that online purchases be paid for online (rather than by check). However, even large companies like Amazon can be hacked, and you don't want anyone getting hold of your credit/debit card or bank account number. If you're going to do online commerce, the safest option is to use a credit card. An even better idea is to have a separate credit card designated only for online payments. If someone makes a fraudulent charge and the credit card company catches them, you can be reimbursed. However, if a hacker takes money directly from your bank account using a debit card or bank account number, you probably won't see that money again. And they will drain your account. Very quickly.
2.5) PayPal is a cool alternative to using credit/debit/bank account numbers online, but it can be hacked too.
Your PayPal account can be hacked, PayPal itself can be hacked, and companies using PayPal for transactions can be hacked so that transactions are rerouted to a different source. You're never safe when engaging in E-commerce.
3) Don't give out personal information. Just don't.
Okay, occasionally you have to give information to a trusted, verifiable source (ex. giving Amazon your home address so they can send you what you ordered). However, your forum friends don't need to know what your full name is (hell, your Facebook friends don't need to know). People often make the mistake of giving out info such as their name, age, address, phone number, personal things about their life and relationships, etc. in public places like forums and social media sites.
A lot of people can use this information against you. First of all, hackers love a good case study. Having all that information really helps when attempting to steal your identity. And second, people can use that information in very negative ways. There are a lot of cool, normal people on the Internet, but there are also a lot of psychopaths (yes, legitimate, clinical psychopaths). As much as we don't want to believe it, people who have tendencies for violent, perverse, and/or predatory behavior exist in society, and they're all on the Internet. And, as in real life, there are more of them than you think. And it generally doesn't take much for them to choose a victim—more than anything, they like a good opportunity and an easy target. You don't want them knowing too much about you, especially if you are of a vulnerable demographic (i.e. female or a young person/minor).
This is why I'm so hesitant to give out information as insignificant as my first name, or even friend people on Facebook. It's not that I believe everyone is a violent criminal/sexual predator; it's that I know these people exist and a lot of times they look and behave like normal, kind people. There's no clear way to tell the difference, so we all need to be cautious as well as courteous and respecting of others' privacy.
4) Don't let someone bully you.
Extending from my last point, if someone is pushing you to give them personal information or access, you'd be wise to have little to do with them. Again, this doesn't automatically mean they're rapists or murderers, but they're bullies and you really don't know what they want, so you'd be best off staying away from them.
On forums or any other website where discussions can be had through comments or posts, if someone is pushing you or someone else around, be assertive, but still courteous. It's okay to defend yourself or someone else. But these online instigators (sometimes called "trolls") love a good fight, and so responding furiously, calling them names and making generalizations, etc. is exactly the kind of response they want from you. That way, they can either make you look bad or they can enjoy the thrill of the argument (yes, some people get a thrill out of this). Don't feed the trolls. Stick up for yourself, and do the same for others, but be responsible and mature. It's far easier said than done, but it's worth it.
Finally, if this person continues to bother you, you can always leave. Unlike real-life situations, the anonymity and geographic differences allow you to simply "walk away" from an argument. Again, sometimes easier said than done, but online fights ruin everyone's day (except for the trolls'; their days are usually pretty crappy anyway—that's why they do this). Don't let them ruin yours.
5) You'll probably be infected by malware at some point.
It doesn't matter how careful you are, what antivirus you have, or whether or not you use a Mac. If you use an Internet-connected computer long enough, you'll be infected by something. Usually, it happens right under your nose. You don't have to download anything, open any weird attachments or click "yes" on any suspicious dialog boxes. If that was the only way malware could get onto your machine, it wouldn't be so rampant. Hackers know how to download malware silently, so your best bet is to follow a few rules:
1) Be vigilant. Always. Get to know how your computer runs normally so you can pick up suspicious activity.
2) Download antivirus/antimalware. In fact, download a couple of programs—it's always good to have a second pair of eyes watching. (Just make sure the programs are compatible with each other.)
3) If your computer begins behaving strangely and you think your programs may be missing something, it doesn't hurt to do a third-party scan. I'd suggest HitmanPro (sorry Mac users; it's not available for OSX yet).
4) Most importantly, don't assume you're safe. A lot of people—amateurs and tech geeks alike—allow their egos get in the way of their safety. You probably use your computer for very important things and send very important information through it. Hackers like to be one step ahead of everyone else, and a lot of them play the game quite well. Cybercrime is evolving as quickly as any other facet of technology. It's up to you to make sure you don't fall behind.
Again, just a general list. If you have any other important points you'd like to share, be my guest and post a comment below. :-)