Cisco Cisco Email Security Appliance C170 사용자 가이드

(once enabled) are “always on,” catching outbreak messages locally before the full anomaly has formed 
on a global basis. Additionally, Adaptive Rules continuously respond to small and subtle changes in 
email traffic and structure, providing updated protection to customers.

A Outbreak Filter rule is basically a Threat Level (e.g. 4) associated with a set of characteristics for an 
email message and attachment — things such as file size, file type, file name, message content, and so 
on. For example, assume the Cisco IronPort SIO notices an increase in the occurrences of a suspicious 
email message carrying a .exe attachment that is 143 kilobytes in size, and whose file name includes a 
specific keyword (“hello” for example). An Outbreak Rule is published increasing the Threat Level for 
messages matching this criteria. Your Cisco IronPort appliance checks for and downloads newly 
published Outbreak and Adaptive Rules every 5 minutes by default (see 

). Adaptive Rules are updated less frequently than Outbreak Rules. On the Cisco IronPort 

appliance, you set a threshold for quarantining suspicous messages. If the Threat Level for a message 
equals or exceeds the quarantine threshold, the message is sent to the Outbreak quarantine area. You can 
also set up a threshold for modifying non-viral threat messages to rewrite any URLs found in suspicious 
messages or add a notification at the top of message body.

 provides a basic set of guidelines or definitions for each of the various levels.

For more information about threat levels and outbreak rules, see 

.

The quarantine threat level threshold allows administrators to be more or less aggressive in quarantining 
suspicious messages. A low setting (1 or 2) is more aggressive and will quarantine more messages; 
conversely, a higher score (4 or 5) is less aggressive and will only quarantine messages with an extremely 
high likelihood of being malicious.

0

None

There is no risk that the message is a threat.

1

Low

The risk that the message is a threat is low.

2

Low/Medium

The risk that the message is a threat is low to medium. It is a 
“suspected” threat.

3

Medium

Either the message is part of a confirmed outbreak or there is a medium 
to large risk of its content being a threat.

4

High

Either the message is confirmed to be part of a large scale outbreak or 
its content is very dangerous.

5

Extreme

The message’s content is confirmed to part of an outbreak that is either 
extremely large scale or large scale and extremely dangerous.