I agree that it would be best to verify an attachment before opening it, but at least for me, I routinely send and receive many file attachments to/from known companies, and generally proceed to open such attachments if there is otherwise nothing suspicious about them. That is what makes Sircam, and similar viruses that propagate based on stored addresses, so insidious. I was hit by Sircam last week from a server in a mainland Chinese company that I deal with all the time. Fortunately McAfee detected and quarantined the virus, but I was rather annoyed nonetheless, as I had specifically inquired whether the company had updated their virus signatures after the initial Sircam outbreak over a month ago. They assured me that they had.