When to trust an e‑mail message
This information applies to Windows Internet Explorer 7 and Windows Internet Explorer 8.
E‑mail is a great way to keep in touch with other people. Unfortunately, it can also open your computer to security risks, computer viruses, and potentially malicious software if you're not careful about the messages and attachments that you open. Before opening any e‑mail message or attachment, be sure that you have an up-to-date antivirus program installed. The antivirus program should be configured to scan messages as they arrive (real-time), and to scan all types of file attachments.
Here are some questions you can ask yourself to help decide whether to open an e‑mail message or attachment.
Is the message from a person or organization that you know and trust? If the message is from someone you've never heard of, be cautious. If it appears to be from someone you know, be suspicious of odd or inappropriate subject lines such as RE: Your archive, or attachments that contain program files (executable files) such as price.exe. Many viruses can mimic e-mail addresses to make it look like the message is from someone you know.
If you know the person or company sending the message, but you've never received e‑mail from them before, make sure you know why you're getting a message now. Check the text in the Subject line and the file name of the attachment, if there is one. If any of that text seems suspicious, delete the message or make sure it is scanned using up-to-date antivirus software before opening it.
Were you expecting a message or attachment from the sender with the subject or file name? If not, send a separate e‑mail message to the sender (don't click Reply) and ask if he or she really sent this e‑mail message.
Junk e‑mail and viruses often use random characters or words in the subject line or attachment file name to bypass content or spam filters. An unexpected message from a friend that has gibberish in the subject line might be sent by a virus that mimics (or spoofs) your friend's e‑mail address. Subject line messages that urge you to do something, for example, "Important! Open the attachment immediately!" might indicate that the e‑mail message might not be safe to open. An attachment with a double file name extension, such as Sample.jpg.exe, is not a file that someone would normally send, and could be a virus.