I'm looking for a list or lists of address blocks / subnets of potentially malicious or unfruitful / known botnets or Google scrapers. The purpose of this is to help to eliminate bot clicks / scrapes and simply unfruitful clicks on AdWords campaigns via the "IP address exclusion" function. Where can I find lists of this nature?
AdWords already does not count visits from the Googlebot or other known search engine crawlers, it is intelligent enough to recognise these as invalid clicks.
As for blocking IP addresses or address blocks this is a bad idea as not all IP's in a block will be dangerous, as well as not all users on an IP will be dangerous.
There is also no reason to specifically take any action yourself to prevent this as Google already runs advanced checks to validate clicks in AdWords before charging you. Google defines Invalid Clicks as...
Examples of invalid clicks that Google specifies include...
Google states in their support portal that each AdWords click is examined by their systems and that invalid clicks and impressions are removed from the account data.
Google also specifically states that while they try to filter invalid clicks from reports and payments if invalid clicks have escaped detection you may be eligible to receive a credit and thyat is referred to as an "invalid activity adjustment".