Not a new visitor at my end but no mention of it here. Looks like marketing people crafted the UA -- here 'tis, in its entirety:
Expanse, a Palo Alto Networks company, searches across the global IPv4 space multiple times per day to identify customers' presences on the Internet. If you would like to be excluded from our scans, please send IP addresses/domains to: scaninfo@paloaltonetworks.com
Never asks for robots.txt
Anyone ever request exclusion?