I understand your concern, but please be informed that McAfee's Virus Research team is constantly updating its library of 'known' viruses and spyware. At the core of McAfee software is something called 'heuristic' protection...which looks for suspect behavior by any program or file. Even so, the constantly-changing nature of viruses and their different variants makes 100% security impossibility, with any anti-virus software. Moreover, McAfee Real time scanner actively scans for any suspicious activities that happens on your computer, hence eventually while you open these kind of attachments there are randomly scanned and if at all any issues found with those files, they would be automatically blocked and quarantined intimating you of the same.
Are you using any E-mail clients like Outlook, Eudora, Outlook Express on your computer to access E-mails?
Nop, I meant the web-based mail services. However, I just wanted to know the procedure by which the McAfee investigates the compressed files which seems to be different from non-compressed ones. (After being downloaded, so I dont mind about the mail service type anyway).
Thanks for conceptual explanation. By the way, the only reason that I posted that question was the fact that I was wondering about the procedure by which the McAfee investigates the compressed files which seems to be different from non-compressed ones. This was the same for some other anti-virus softwares which I tried. It might relate to the different structure of RAR-ZIP files "OR" the fact that those suspicious files are Trojans that are not avoided by McAfee completely.