I see in Release Note application update in Dynamic Updates or email like this :
There is a maximum PAN-OS version in Conficker.
Why some threat have limitation in PAN-OS ?
checked the older "Content Update" emails from paloalto. if you take a look you will see, that new signatures depends on a minimum OS version.
And, some modified signatures are depended from a minimum to maximum OS version. So the signature will be detected as well in newer version, but the modification of the signature is only for the OS version between min and max.
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