Что сие значит? (агенты в robots.txt)

Господа, кто знает, что это за User-agent-ы? От чего это народ так защищается?

User-agent: ia_archiver

Disallow: /

User-agent: Black Hole

Disallow: /

User-agent: Titan

Disallow: /

User-agent: WebStripper

Disallow: /

User-agent: NetMechanic

Disallow: /

User-agent: CherryPicker

Disallow: /

User-agent: EmailCollector

Disallow: /

User-agent: EmailSiphon

Disallow: /

User-agent: WebBandit

Disallow: /

User-agent: EmailWolf

Disallow: /

User-agent: ExtractorPro

Disallow: /

User-agent: CopyRightCheck

Disallow: /

User-agent: Crescent

Disallow: /

User-agent: Wget

Disallow: /

User-agent: SiteSnagger

Disallow: /

User-agent: ProWebWalker

Disallow: /

User-agent: CheeseBot

Disallow: /

User-agent: Teleport

Disallow: /

User-agent: TeleportPro

Disallow: /

User-agent: MIIxpc

Disallow: /

User-agent: Telesoft

Disallow: /

User-agent: Website Quester

Disallow: /

User-agent: WebZip

Disallow: /

User-agent: moget/2.1

Disallow: /

User-agent: WebZip/4.0

Disallow: /

User-agent: WebSauger

Disallow: /

User-agent: WebCopier

Disallow: /

User-agent: NetAnts

Disallow: /

User-agent: Mister PiX

Disallow: /

User-agent: WebAuto

Disallow: /

User-agent: TheNomad

Disallow: /

User-agent: WWW-Collector-E

Disallow: /

User-agent: RMA

Disallow: /

User-agent: libWeb/clsHTTP

Disallow: /

User-agent: asterias

Disallow: /

User-agent: httplib

Disallow: /

User-agent: turingos

Disallow: /

User-agent: spanner

Disallow: /

User-agent: Harvest/1.5

Disallow: /

User-agent: Bullseye/1.0

Disallow: /

User-agent: Crescent Internet ToolPak HTTP OLE Control v.1.0

Disallow: /

User-agent: CherryPickerSE/1.0

Disallow: /

User-agent: CherryPickerElite/1.0

Disallow: /

User-agent: WebBandit/3.50

Disallow: /

User-agent: NICErsPRO

Disallow: /

User-agent: DittoSpyder

Disallow: /

User-agent: lwp-trivial

Disallow: /

User-agent: Wget

Disallow: /

User-agent: BunnySlippers

Disallow: /

User-agent: LinkWalker

Disallow: /

User-agent: cosmos

Disallow: /

User-agent: moget

Disallow: /

User-agent: hloader

Disallow: /

User-agent: humanlinks

Disallow: /

User-agent: LinkextractorPro

Disallow: /

User-agent: Offline Explorer

Disallow: /

User-agent: Mata Hari

Disallow: /

User-agent: Web Image Collector

Disallow: /

User-agent: The Intraformant

Disallow: /

User-agent: BlowFish/1.0

Disallow: /

User-agent: MIIxpc/4.2

Disallow: /

User-agent: BuiltBotTough

Disallow: /

User-agent: ProPowerBot/2.14

Disallow: /

User-agent: BackDoorBot/1.0

Disallow: /

User-agent: toCrawl/UrlDispatcher

Disallow: /

User-agent: WebEnhancer

Disallow: /

User-agent: suzuran

Disallow: /

User-agent: VCI WebViewer VCI WebViewer Win32

Disallow: /

User-agent: VCI

Disallow: /

User-agent: Szukacz/1.4

Disallow: /

User-agent: QueryN Metasearch

Disallow: /

User-agent: Openfind data gathere

Disallow: /

User-agent: Openfind

Disallow: /

User-agent: Xenu's Link Sleuth 1.1c

Disallow: /

User-agent: Xenu's

Disallow: /

User-agent: Zeus

Disallow: /

User-agent: RepoMonkey Bait & Tackle/v1.01

Disallow: /

User-agent: RepoMonkey

Disallow: /

User-agent: Zeus 32297 Webster Pro V2.9 Win32

Disallow: /

User-agent: Webster Pro

Disallow: /

User-agent: LinkScan/8.1a Unix

Disallow: /

User-agent: Keyword Density/0.9

Disallow: /