Trend Micro InterScan M Series, Administrator'S Manual

Page: 319 / 480

Technical Support, Troubleshooting, and FAQs
14
-
17
If the file is not big enough to trigger large-file handling settings, the file will be
scanned as a normal file.
When downloading a large file, the time to download the file and scan it for viruses
may be long enough to cause the browser to time out.
Tip: Trend Micro recommends not scanning uncompressed files larger than 50 MB
(default value); however, these values may vary depending on your network
speed, server capability, and security requirements.
InterScan Gateway Security Appliance provides the following methods to address
large-file scan lag when downloading HTTP and FTP files:
• Do not scan files larger than sets the maximum file size for scanning. InterScan
Gateway Security Appliance will not scan files larger than the size specified. The
default is 50MB.
WARNING! This option effectively allows a hole in your Web security—large files will not
be scanned. Trend Micro recommends that you choose this option only on a
temporary basis.
Deferred scan: (moderate risk) InterScan Gateway Security Appliance receives a file
and begins scanning while it loads part of the page. To keep the connection with the
client alive for the time it takes to scan the large file, InterScan Gateway Security
Appliance "trickles", or delivers a small amount of the file to the requesting client.
InterScan Gateway Security Appliance will stop the connection if it finds a virus.
Note: This option is considered "moderate risk" because it is possible that malicious code
will be delivered to the client machine as part of the unscanned delivery.
Most files, however, are unreadable until the entire file is reconstructed.