Dug into those weird URLs some more today, and it just gets more and more weird. There is some kind of worm that hacks into vulnerable older websites, and injects them with new code.
As noted above, there are the sites that have a directory/folder added, filled with php pages of keyword phrases.
Then, new to me, there are sites that are also injected with dozens of links pointing out to those pages. The links use the word that the keyword page targets as anchor text, and are invisible - hidden in the code of the unwitting sites' homepages.
Two examples:
http://sfmfiles.net/and
http://fcmrepresentation.com/Open them up in a browser - you won't see anything weird. But go to View>Page Source (or Source in IE) and look at the code: you'll see a huge list of hidden links. These all point to keyworded directories, pages like the original ones I posted above.
I randomly checked one of these pages, about "vaccines" to see where else it was getting links from - and found over 160 inbound links, all using "vaccines" as anchor text. All of the sites linking to it use the hidden links method, invisible until you look at the source code.
http://1tre.dk/zjnef/vaccines.php is linked to from the following pages:
http://www.unrarx.com/
http://tnchick.com/
http://www.thocp.net/
http://www.deepred.co.uk/
http://www.historyexplained.com/
http://www.chichi.org/
http://www.digitalsoundmagic.com/
http://www.akomplice-clothing.com/
http://www.plantationchamber.org/
http://www.aqua-adventures.com/
http://www.gulker.com/
http://www.x-traonline.org/
http://www.emint.com/
http://ohbitchpleez.com/
http://www.altacam.com/
http://www.davidsoul.org/
http://www.scoutingvirginia.org/
http://www.tinceiling.org/
http://www.blackjackbuffers.com/
http://www.reillyraiders.org/
http://www.kouroshotelmykonos.gr/
http://www.aipilotshop.com/
http://www.sitenames.com/
http://www.woodstockfolkmusic.com/
http://www.housepro.net/
http://www.buzmob.com/
http://criticalcompendium.com/
http://www.bruceleecentral.com/
http://www.karlkemp.com/
http://www.photobirder.com/
http://www.boulevardflorist.com/
http://www.odysseytransportation.com/
http://www.plasticsurgerytexas.com/
http://www.pet-memorial-markers.com/
http://www.hutsachs.com/
http://www.mcgeespub.com/
http://arieljvan.com/
http://www.dictionaryofsign.com/
http://www.valerielandsburg.com/
http://www.artmonster.com/
http://www.sluka.com/
http://frizzensparks.org/
http://www.keystroketechnology.com/
http://aristide.org/
http://www.doverelease.com/
http://www.specialteamssolutions.com/
http://www.jcmcf.org/
http://www.nivb.com/index.php
http://projectfilmschool.org/
http://www.gothinkblog.com/
http://www.westminsterpc.com/
http://ncmc.net/
http://www.greggy.net/
http://www.chaos-studios.net/
http://www.bataancvl29.org/
http://www.thecivilrightonline.com/
http://deepred.com/
http://www.stmarksmillsboro.org/
http://www.compusaveconsulting.com/
http://www.dat-sa.com/
http://provocativeplanet.com/
http://teamkarma.com/
http://chicagofans.org/
http://www.guapucheros.com/
http://www.andromedaroom.com/
http://usfwi.org/
http://esecaucus.com/
http://www.higginsstudios.com/
http://jokay.com.au/2009/05/20/jos-lifestream-daily-digest-120/
http://agt.id.au/
http://lunardoll.com/
http://cmashmusic.org/
http://www.robgroup.com/
http://www.ditditdot.com/
http://www.longleafcove.com/
http://www.dishstore.net/index.php
http://thericksniderreport.com/uncategorized/was-eaglebank-bowl-half-full-or-empty/
http://www.dishstore.net/index.php?cPath=57
http://www.prison-fellowship.no/
http://arieljvan.com/2009/08/29/religion-saves-mark-driscoll/
http://nwbm.org/
http://livesaysinc.com/
http://www.gulker.com/about-2/
http://www.dishstore.net/index.php?cPath=26
http://www.dishstore.net/index.php?cPath=22
http://www.dishstore.net/index.php?cPath=51
http://www.dishstore.net/index.php?cPath=65
http://www.dishstore.net/index.php?cPath=73
http://www.dishstore.net/index.php?cPath=67
http://www.dishstore.net/index.php?cPath=53
http://www.gulker.com/chris-gulker-photo-archive/
http://www.gulker.com/hidden-from-pages-sidebar-list/p2-aka-the-paperless-project/
http://www.gulker.com/wp/2008/02/04/microsoft-google-yahoo-and-apple/
http://www.gulker.com/wp/2010/01/11/stumping-our-way-through-a-good-full-day/
http://bendigophotos.com/
http://asterisk-cafe.com/
http://windingroadrecords.com/
http://www.craigslistconsultant.com/
http://www.gulker.com/columns/
http://www.gulker.com/nikon-d50-body/
http://www.dishstore.net/index.php?cPath=52
http://www.dishstore.net/index.php?cPath=54
http://www.dishstore.net/index.php?cPath=59
http://www.dishstore.net/index.php?cPath=75
http://www.townofgroton.org/main?cmd=schools-grotoncomm
http://www.gulker.com/wp/2007/08/
http://www.gulker.com/wp/2008/01/
http://www.gulker.com/wp/2008/04/
http://www.gulker.com/wp/2009/04/
http://www.gulker.com/wp/2007/07/
http://www.gulker.com/wp/2007/12/
http://www.gulker.com/wp/2007/01/
http://www.gulker.com/wp/2008/05/
http://www.gulker.com/wp/2009/06/
http://www.aardvarkwebdesigns.com/
http://www.clintonstreet.org/
http://www.writinganalysis.com/
http://www.backgame.com/
http://www.asigncompany.com/
The web of sites involved in this operation is insanely vast - the more I dig in, the more the labyrinth of links expands.
What I have yet to find is a target of all this manipulation: clearly, someone is trying to build up authority for a wide variety of keyphrases, presumably to point appropriate pages to some kind of content that they want to rank highly for some combination of the keywords employed. I don't know if the wide variety of keywords is just to have a huge bucket of possible words to bring to bear to undetermined future ranking efforts, or if the massive web of keyphrases simply hides the few that are being used ...
I don't even know if this tactic has a shot at succeeding - in theory, Google would not count the invisible links, and would not give the affected pages any weight - meaning that when they were in turn pointed at a page it should not give a rankings boost ...
Anyway, if anyone else gets curious about this and finds anything new out, let me know.