Detecting 'stealth' web-crawlers

Question

What options are there to detect web-crawlers that do not want to be detected?

(I know that listing detection techniques will allow the smart stealth-crawle

Answer 1

Untested, but here is a nice list of user-agents you could make a regular expression out of. Could get you most of the way there:

ADSARobot|ah-ha|almaden|aktuelles|Anarchie|amzn_assoc|ASPSeek|ASSORT|ATHENS|Atomz|attach|attache|autoemailspider|BackWeb|Bandit|BatchFTP|bdfetch|big.brother|BlackWidow|bmclient|Boston\ Project|BravoBrian\ SpiderEngine\ MarcoPolo|Bot\ mailto:craftbot@yahoo.com|Buddy|Bullseye|bumblebee|capture|CherryPicker|ChinaClaw|CICC|clipping|Collector|Copier|Crescent|Crescent\ Internet\ ToolPak|Custo|cyberalert|DA$|Deweb|diagem|Digger|Digimarc|DIIbot|DISCo|DISCo\ Pump|DISCoFinder|Download\ Demon|Download\ Wonder|Downloader|Drip|DSurf15a|DTS.Agent|EasyDL|eCatch|ecollector|efp@gmx\.net|Email\ Extractor|EirGrabber|email|EmailCollector|EmailSiphon|EmailWolf|Express\ WebPictures|ExtractorPro|EyeNetIE|FavOrg|fastlwspider|Favorites\ Sweeper|Fetch|FEZhead|FileHound|FlashGet\ WebWasher|FlickBot|fluffy|FrontPage|GalaxyBot|Generic|Getleft|GetRight|GetSmart|GetWeb!|GetWebPage|gigabaz|Girafabot|Go\!Zilla|Go!Zilla|Go-Ahead-Got-It|GornKer|gotit|Grabber|GrabNet|Grafula|Green\ Research|grub-client|Harvest|hhjhj@yahoo|hloader|HMView|HomePageSearch|http\ generic|HTTrack|httpdown|httrack|ia_archiver|IBM_Planetwide|Image\ Stripper|Image\ Sucker|imagefetch|IncyWincy|Indy*Library|Indy\ Library|informant|Ingelin|InterGET|Internet\ Ninja|InternetLinkagent|Internet\ Ninja|InternetSeer\.com|Iria|Irvine|JBH*agent|JetCar|JOC|JOC\ Web\ Spider|JustView|KWebGet|Lachesis|larbin|LeechFTP|LexiBot|lftp|libwww|likse|Link|Link*Sleuth|LINKS\ ARoMATIZED|LinkWalker|LWP|lwp-trivial|Mag-Net|Magnet|Mac\ Finder|Mag-Net|Mass\ Downloader|MCspider|Memo|Microsoft.URL|MIDown\ tool|Mirror|Missigua\ Locator|Mister\ PiX|MMMtoCrawl\/UrlDispatcherLLL|^Mozilla$|Mozilla.*Indy|Mozilla.*NEWT|Mozilla*MSIECrawler|MS\ FrontPage*|MSFrontPage|MSIECrawler|MSProxy|multithreaddb|nationaldirectory|Navroad|NearSite|NetAnts|NetCarta|NetMechanic|netprospector|NetResearchServer|NetSpider|Net\ Vampire|NetZIP|NetZip\ Downloader|NetZippy|NEWT|NICErsPRO|Ninja|NPBot|Octopus|Offline\ Explorer|Offline\ Navigator|OpaL|Openfind|OpenTextSiteCrawler|OrangeBot|PageGrabber|Papa\ Foto|PackRat|pavuk|pcBrowser|PersonaPilot|Ping|PingALink|Pockey|Proxy|psbot|PSurf|puf|Pump|PushSite|QRVA|RealDownload|Reaper|Recorder|ReGet|replacer|RepoMonkey|Robozilla|Rover|RPT-HTTPClient|Rsync|Scooter|SearchExpress|searchhippo|searchterms\.it|Second\ Street\ Research|Seeker|Shai|Siphon|sitecheck|sitecheck.internetseer.com|SiteSnagger|SlySearch|SmartDownload|snagger|Snake|SpaceBison|Spegla|SpiderBot|sproose|SqWorm|Stripper|Sucker|SuperBot|SuperHTTP|Surfbot|SurfWalker|Szukacz|tAkeOut|tarspider|Teleport\ Pro|Templeton|TrueRobot|TV33_Mercator|UIowaCrawler|UtilMind|URLSpiderPro|URL_Spider_Pro|Vacuum|vagabondo|vayala|visibilitygap|VoidEYE|vspider|Web\ Downloader|w3mir|Web\ Data\ Extractor|Web\ Image\ Collector|Web\ Sucker|Wweb|WebAuto|WebBandit|web\.by\.mail|Webclipping|webcollage|webcollector|WebCopier|webcraft@bea|webdevil|webdownloader|Webdup|WebEMailExtrac|WebFetch|WebGo\ IS|WebHook|Webinator|WebLeacher|WEBMASTERS|WebMiner|WebMirror|webmole|WebReaper|WebSauger|Website|Website\ eXtractor|Website\ Quester|WebSnake|Webster|WebStripper|websucker|webvac|webwalk|webweasel|WebWhacker|WebZIP|Wget|Whacker|whizbang|WhosTalking|Widow|WISEbot|WWWOFFLE|x-Tractor|^Xaldon\ WebSpider|WUMPUS|Xenu|XGET|Zeus.*Webster|Zeus [NC]

Taken from: http://perishablepress.com/press/2007/10/15/ultimate-htaccess-blacklist-2-compressed-version/

Answer 2

An easy solution is to create a link and make it invisible

<a href="iamabot.script" style="display:none;">Don't click me!</a>

Of course you should expect that some people who look at the source code follow that link just to see where it leads. But you could present those users with a captcha...

Valid crawlers would, of course, also follow the link. But you should not implement a rel=nofollow, but look for the sign of a valid crawler. (like the user agent)

Answer 3

A while back, I worked with a smallish hosting company to help them implement a solution to this. The system I developed examined web server logs for excessive activity from any given IP address and issued firewall rules to block offenders. It included whitelists of IP addresses/ranges based on http://www.iplists.com/, which were then updated automatically as needed by checking claimed user-agent strings and, if the client claimed to be a legitimate spider but not on the whitelist, it performed DNS/reverse-DNS lookups to verify that the source IP address corresponds to the claimed owner of the bot. As a failsafe, these actions were reported to the admin by email, along with links to black/whitelist the address in case of an incorrect assessment.

I haven't talked to that client in 6 months or so, but, last I heard, the system was performing quite effectively.

Side point: If you're thinking about doing a similar detection system based on hit-rate-limiting, be sure to use at least one-minute (and preferably at least five-minute) totals. I see a lot of people talking about these kinds of schemes who want to block anyone who tops 5-10 hits in a second, which may generate false positives on image-heavy pages (unless images are excluded from the tally) and will generate false positives when someone like me finds an interesting site that he wants to read all of, so he opens up all the links in tabs to load in the background while he reads the first one.

Answer 4

People keep addressing broad crawlers but not crawlers that are specialized for your website.

I write stealth crawlers and if they are individually built no amount of honey pots or hidden links will have any effect whatsoever - the only real way to detect specialised crawlers is by inspecting connection patterns.

The best systems use AI (e.g. Linkedin) use AI to address this.
The easiest solution is write log parsers that analyze IP connections and simply blacklist those IPs or serve captcha, at least temporary.

e.g.
if IP X is seen every 2 seconds connecting to foo.com/cars/*.html but not any other pages - it's most likely a bot or a hungry power user.

Alternatively there are various javascript challenges that act as protection (e.g. Cloudflare's anti-bot system), but those are easily solvable, you can write something custom and that might be enough deterrent to make it not worth the effort for the crawler.

However you must ask a question are you willing to false-positive legit users and introduce inconvenience for them to prevent bot traffic. Protecting public data is an impossible paradox.

Answer 5

See Project Honeypot - they're setting up bot traps on large scale (and have DNSRBL with their IPs).

Use tricky URLs and HTML:

<a href="//example.com/"> = http://example.com/ on http pages.
<a href="page&amp;&#x23;hash"> = page& + #hash

In HTML you can use plenty of tricks with comments, CDATA elements, entities, etc:

<a href="foo<!--bar-->"> (comment should not be removed)
<script>var haha = '<a href="bot">'</script>
<script>// <!-- </script> <!--><a href="bot"> <!-->