Attachments may contain viruses or Trojans. First save the attachment to a file, then check it with your antiviral kit. Be on your guard. You don't have to believe all the scary new virus warnings on the Web, especially if the warning tells you to forward it to all your friends. Update your antiviral databases at least every 3-5 days.
Most antiviral kits provide free updates on the Web.
If your antiviral database has not been updated in three months, the efficiency of your antiviral software is drastically reduced. Inexplicable file changes or new files found by that software are signs of a new virus or a Trojan. Remember that a change of password won't help if your authentication details have been stolen by a Trojan. The Trojan will be stealing them again and again until it is removed from your computer. So have an antiviral kit installed if you don't already have one.