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Symantec keeps blocking traffic from the IP of my Comcast SMC Network gateway. It blocks traffic because it is detecting a UDP Flood Attack. According to the log the CPU usage is spiking to 100% when this attack occurs but Im not seeing this spike in the performance monitor. Symantec also detects a UDP Flood Attack when I am connected to my home network from what I assume is my home modem.

Is this a legitimate attack or a false positive? What could I do to stop the attacks?

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If it's blocking the traffic from your external IP that doesn't necessarily mean it's coming from your gateway. Any traffic that's NAT'd will come out with the public IP (the IP of your gateway). I would make sure there's no possibility that a computer in your LAN is infected. – DKNUCKLES Apr 12 '12 at 17:59
up vote 5 down vote accepted

A useful first step would be to use something like wireshark to see if you actually have high levels of UDP traffic.

If so, it could be real. If not it may well be a false positive, so you'd then need to do some more digging.

Also, try the performance monitor from SysInternals (Process Explorer) - just in case there is an issue with your existing one.

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In addition to Process Explorer, try Process Monitor (from SysInternals as well) which can be used to filter for ANYTHING that uses UDP packets. – logicalscope Apr 12 '12 at 16:46

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