I get file attachments from both friends and strangers. Should I just open the ones from friends?

I would even think twice before opening file attachments from friends. What if your friend's computer has been infected by a virus, and the virus emails you a message with itself attached? You get the email, think it's from your friend, and open the attachment. *Poof!* Your computer is now infected!

The only time you should open an attachment even from a friend is if it is a file type that can't carry viruses (generally speaking you can open image files, but even with those, believe it or not, someone developed a virus to attach to an image (read below for a question and answer about that).

If you have any doubt about whether a file type can carry a virus, don't open the email. Call or email your friend and say "Did you send me this file?" If they say no, obviously you aren't going to open it. And if the message is from a stranger? Don't open it at all! I occasionally get resumes from people who want to work for me, and rather than mailing them, they send them as Microsoft Word Documents. I don't know them from Adam, and I won't open their attachments.

I get emails with picture files (stuff with .gif?x=5, .bmp, and .jpg?x=5 file extensions) attached. I know there are some kinds of email attachments I should never open; what about these? Can I get infected through these?

Well...yes, technically, it is possible, but only under the following scenario. Your computer has to already be infected with another virus whose purpose is to act as interpreter for the image virus. Seems kind of pointless to me. (The "Perrun Virus" was an example of this kind of virus, which attached to jpg files. A lot of hype, not much action)

However, you still need to be careful when opening images attached to emails. Be sure that the file extension really is an image extension (the ones you listed, plus a few others). I've seen emails come in with file names like "yourpicture.jpg?x=5.exe". Clever. The extension isn't really 'jpg', it's 'exe', and you already know you should never open those. And remember: if the attachment is from someone you don't know, why would you bother opening it anyway?

Is it okay to put my credit card number, expiration date, and other information in an email? I'd like to purchase a product online, and they want me to put my credit card info on their website; is it really any different to put it in an email?

Actually, this question is the one that finally convinced me it was time to create my Q&A website. I was absolutely horrified yesterday to receive an email from a potential customer who wanted to buy one of my products, and had put his credit card number, expiration date and name in his email to me! Never, never, never do this! Don't even think about it! People tend to think that email is a private correspondence between them and their intended recipient. That would be a nice theory, but it is not guaranteed!

Remember that emails do not send or receive over secure sockets, which means if someone was looking and analyzing in the right place at the right moment, they could intercept your data packets and snag your credit card number. Where your credit card number is concerned, it is better to be paranoid than sorry.

I'm kind of annoyed that after buying my AntiVirus software, the company is hitting me up for a "subscription renewal"? What in blue blazes is that, and do I really need to do it?

Yes, you need to keep renewing your subscription. It's one of the most painful expenses you'll face each year--not because it costs so much (all things considered, it really isn't so bad) but because it's a fee you have to pay for the malice and moral bankruptcy of the virus creators.

See, that yearly fee you pay helps to pay the costs of all the teams of computer geeks who are working to circumvent the viruses that are being cranked out on a daily basis. You may say "But it's not fair that I have to pay for someone else's deviant behavior." And you would be exactly right in saying that. It isn't fair.

But it also isn't fair to ask a software company to protect your computer from new viruses every day for free either. You see, every time a new virus is invented, some software developer has do design a way of capturing and removing that virus. And guess what! Software developers don't work for free, and we shouldn't expect them to! So, grin and bear it, and keep reminding yourself, not a penny of that money goes to the guy who invented the virus.

My AntiVirus software keeps talking about downloading "virus definitions". I don't understand what that means, or why I would want to do it. Can you explain?

When dealing with biological viruses, you want to have an antibody, which will either protect you from being infected or, if you've already been infected, it will start killing off the virus. But there isn't one antibody that works for all viruses, which is why scientists are always working to find new ways to combat new viruses. Computer viruses are very similar. A virus definition is like an antibody. It's really just information about a particular virus, which will help the virus software fight the virus, or protect you from infection. And just like each biological virus requires a different antibody, each computer virus requires a virus definition. Do you want to download the virus definition files whenever your computer recommends that you do so? Absolutely!