Did someone you know just send you an electronic mail attachment that you weren't expecting? Perhaps it's a picture to go along with a joke, a song they want you to hear, or a program that displays fireworks on your screen. Surely your co-worker checked the file out first? Of course your mom would not send you a file that would harm your computer, right?
Nowadays, no matter who you think sent an e-mail attachment, you MUST be safe. Before opening a surprise attachment, why not first ask your friend, coworker, or family member in a friendly e-mail if they really meant to send you the file?
Why am I saying this? It's not to upset dear ma. However, thanks to viruses that spread through e-mail, not to mention other types of malware people might unknowingly install by visiting rogue or hacked websites, many peoples' computers are becoming unwitting accomplices to the spread of rogue file attachments. There are viruses that can infect machines causing them to e-mail innocent looking attachments that are actually viruses or spyware to everyone in their address book. Worse yet, some of this malware actually can make the e-mail look as if it came from someone else entirely!
That's right. For sake of argument, assume you have a friend, Bob, who uses e-mail software that contains an address book. Let's say that your name is in Bob's address book, as well as the name of a mutual friend, Bill. Unfortunately, there is malware that can cause e-mail to be sent to you, unknowingly by Bob, that is made to look like it originally came from Bill! As you can see, even if your friend, family member, or coworker is not directly infected by a virus, you may receive rogue attachments that seem to be originated by them.
"Ok, ok," you may be thinking. "I understand to be wary of executable attachments. But what about photos, songs, and documents. These are safe to open - right?"
Wrong. Virtually any type of rogue attachment can cause problems.
First, realize that depending on your configuration, Windows does not always display file extensions, the characters at the end of a filename that determine its file type. Just because you receive what you think is a music file does not mean it is actually a song. Double-click an application pretending to be a song and instead of your media player opening up, a virus may get installed on your machine.
Second, some rogue file attachments may be written to take advantage of security exploits found in popular software you may have installed. Rogue Word, Excel, PowerPoint, and other Office files may contain what are called Macro viruses, which when run could do all sorts of damage to your machine.
If an exploit exists in a popular multimedia player such as QuickTime for Windows, Winamp, or Windows Media Player and the software has not been patched on your machine, double-clicking a rogue music file could take advantage of the exploit if that happens to be your default player. The same goes with images, photos, and videos - if there's a bug with an image viewer, for example, a hacker may have constructed a picture to take advantage of this problem. If you unluckily view the rogue attachment with the software that contains a security hole, many problems could arise.
Keeping your operating system and software up-to-date can help prevent, but not completely eliminate, these types of attacks.
When it comes to e-mail attachments, be safe. Scan EVERY e-mail attachment no matter who you think is its originator. Know that executables are not the only types of attachments that are theoretically dangerous, so be careful with songs, images, and documents as well. Don't open an e-mail attachment unless you're sure it is safe and you confirm the sender meant to e-mail you the file. Keeping your virus scanner up-to-date may help, too :)
