Unless you subscribe to a newsletter that issues virus warnings, you'll rarely get a genuine virus warning from any company or anyone. If you do, it will be from someone you know, but check it out carefully. The vast majority of those are hoaxes.
The myth about US Postal Service adding a 5 cent surcharge to email messages, and urging people to pass it on is still circulating. USPS has no taxing authority -- it has not even been a government agency for many years. The FCC regulates email, but that doesn't stop people from passing on the hoax about USPS.
Hoaxes waste the time and effort of all the people they're forwarded to, and they waste Internet resources. Some are designed to get you to delete legitimate files on your own computer. You can spot most hoaxes and myths by their urgent title, poor grammar, misspelling or wild claims -- they're simply juvenile.Most are forwarded from someone you know. Don't let that fool you. If you're in doubt, but think you really ought to forward one to your friends, please check it out first. [Hoax Database] [Symantec] [ Vmyths.com]
A message that urges you to delete a "infected" file from your computer, and forward the message to everyone you know. The file is actually a needed system file. Two examples are the "sulfnbak.exe" file and "jdbgmgr.exe" files. Both of these have been the subject specious virus warnings. If you've already deleted the file, Microsoft has instructions for restoring it.
Another trick is to attach a worm to a message that claims it is a patch or removal tool for a well known virus or worm. The attachment is actually the virus or worm itself.