Viruses are being passed around within PDF files attached to email messages...

Adobe's popular PDF file format (Portable Document Format) is not susceptible to computer viruses itself. However, files attached to (or embedded within) PDF documents can carry viruses. For example, one of these viruses is a visual basic script (.vbs) file, embedded within a PDF file, that will identify up to 100 contacts in the user’s Outlook program (after searching the address book, contact list, inbox, and sent mail) and send the virus to those contacts.

The first strain of these viruses is reported to only affect those who use the full-blown Adobe Acrobat document creation software, and to not affect users who have just Adobe Reader (which is pre-installed on most computers). However, newer strains of PDF viruses have been reported to execute in Adobe Reader as well.

Unfortunately, most anti-virus programs are just beginning to detect this kind of virus. Anti-virus makers are quickly working on modifications to their scanners that will search for, detect, and remove these new kinds of virus infections. These updates should be included in your regular anti-virus updates.

If you receive an email from someone you don't know and it has a PDF file attached to it, you should delete it immediately, just as you would with any other suspicious email from an unknown sender.

If you receive an email from a friend, family member, co-worker, or someone you do know and it has a PDF file attached, you should open up a new email, and write the person back who sent it to you, asking why they sent you a PDF file and what it's purpose is, before you open it. As noted, the sender may have already been infected by a PDF file virus, and it might have sent itself to you automatically, and addressed itself as the sender, without the sender even knowing it.

To-date, the only safe email file attachments are pure images, such as jpg, jpeg, gif and bmp image files. Most other file types, especially exe, zip, bat, com, vbs, js, jre, and now even pdf files, could possibly be infected.

In summary, as anti-virus makers become more effective at killing viruses, virus makers come up with even more ways to try and infect your computer. You should always be suspicious of any emails you receive that have file attachments, as any of them could be infected even if they are reported to be clean. Therefore, you should always write back the sender directly yourself, asking if the sender actually sent the email themselves. Do not simply reply to the suspect email, as its return address could be phony, it's always best to write back to the person using a new message for confirmation.