Botnet traffic is an artificial traffic generated from thousand of infected zombies PCs - some botnet may count more than one million PCs - and aiming, among other things, at generating fraudulent advertising revenue through click fraud and impression fraud.
Zombie PCs are a "mafia practice" by which PCs are hacked with trojan horse programs. Visits and clicks are made on the PC without the owner being aware. Even if a user was sitting at the computer, he would not see the hidden browser.
In February 2013, Spider.io discovered a botnet called Chameleon which emulated human visitors on 202 selected websites. According to Spider.io estimates:
Chameleon counted 120 000 of host machines
the botnet caused 9 billions of display ad impressions to be served per month to infected PCs
the botnet generated an average click-through rate of 0.02%
the monthly cost to advertisers of ad impressions served to the botnet was at least $6.2 million.
What happens when the Adaptive Security Appliance (ASA) has the Botnet Traffic Filter License that has expired after it's valid term of one year? Does the Botnet Traffic Filter feature work as it did when the License was active?
No. The Botnet Traffic Filter feature gets disabled when the license expires and so you will no longer be able to block any traffic and the ASA will function without the traffic filter enabled.