To configure the firewall to take a packet capture (pcap) when it detects a threat, enable packet capture on Antivirus, Anti-Spyware, and Vulnerability Protection security profiles.
Take a Threat Packet Capture
Enable the packet capture option in the security profile. Some security profiles allow you to define a single-packet capture, or extended-capture. If you choose extended-capture, define the capture length. This will allow the firewall to capture more packets to provide additional context related to the threat. The firewall can only capture packets if the action for a given threat is set to allow or alert. Select Objects > Security Profiles and enable the packet capture option for the supported profiles as follows: Antivirus —Select a custom antivirus profile and in the Antivirus tab select the Packet Capture check box. Anti-Spyware —Select a custom Anti-Spyware profile, click the DNS Signatures tab and in the Packet Capture drop-down, select single-packet or extended-capture. Vulnerability Protection —Select a custom Vulnerability Protection profile and in the Rules tab, click Add to add a new rule, or select an existing rule. Set Packet Capture to single-packet or extended-capture. Note that if the profile has signature exceptions defined, click the Exceptions tab and in the Packet Capture column for a signature, set single-packet or extended-capture. (Optional) If you selected extended-capture for any of the profiles, define the extended packet capture length. Select Device > Setup > Content-ID and edit the Content-ID Settings. In the Extended Packet Capture Length (packets) section, specify the number of packets that the firewall will capture (range is 1-50; default is 5). Click OK.
Add the security profile (with packet capture enabled) to a Security Policy rule. Select Policies > Security and select a rule. Select the Actions tab. In the Profile Settings section, select a profile that has packet capture enabled. For example, click the Antivirus drop-down and select a profile that has packet capture enabled.
View/export the packet capture from the Threat logs. Select Monitor > Logs > Threat. In the log entry that you are interested in, click the green packet capture icon in the second column. View the packet capture directly or Export it to your system.

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