Firewalls don't generally screen computer viruses, though some firewall products may allow for virus-scanning plug-ins. There are also "viruswalls" that scan for viruses at the Internet gateway. Some such products can scan incoming and outgoing E-mail attachments, ftp'd or http'd files etc. for viruses. MIMESweeper, uses yout favourite scanner for scanning the viruses after it has opened up the E-Mail attachments in a secure area on the hard drive of the NT machine. Obviously, the on-demand scanner is an additional cost. MIMESweeper has advanced content filtering abilities which go beyond its capabilities (with assistance from other software) for detection of file viruses and trojans. These products do real scanning before the mail hits the workstation hard drive but make sure your mail attachments, WWW downloads etc. can't be automatically executed and use a good TSR/VXD in combination with a good on-demand scanner. Note that realtime virus scanning at the gateway can add a heavy network overhead and probably won't catch as many viruses as checking *all* files from *all* sources with a desktop scanner. Current informed thinking tends to be that detection of viruses at the firewall is acceptable (1) if you can afford the additional hardware, software and latency (processing overhead), not to mention the hidden administrative overheads of configuration and policy for dealing with boundary conditions such as unusual 7-bit encoding formats, encrypted files etc. (2) as long as you appreciate that it can only be supplementary to checking at the desktop, not a replacement. Mail attachments, FTP and HTTP are more significant vectors for virus transmission than formerly, especially with the near-exponential boom in macro viruses, but other vectors (especially floppy disks) are still of vital concern. System administrators are attracted by the fact that it's easier to update server software than control the use of scanning on individual workstations, but the fact remains that in most environments, until the desktop is adequately protected with good, up-to-date realtime (on-access) scanning and/or scheduled on-demand scanning
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