Major Hacks Into WordPress [HELP?]

So I recently saw some unauthorized files in my folders, including index.php files that contained odd code, which actually redirected to another site.

I called my host [GoDaddy] and believe it or not, they don’t keep FTP logs. I changed my password, but lo-and-behold, the unauthorized files continue to be added.

I was just about to give up, until I took a look at the backlinks going to my site.

It appears that this is a massive-scale hacking attempt across multiple sites, and all of them have happened within the last few weeks. I’m not sure if all of the sites are wordpress sites, but most of them are, which makes me think there must be some sort of vulnerability somewhere.

Of course, I’ve deleted the files, and (fingers crossed) they won’t reappear, but I have a list of all of the sites that contain the weird links in the footer. Is there some sort of common vulnerability that they all have? I’m tearing my hair out trying to figure it out [note the hidden links in the code in the footer]?

http://stephanie.materns.com/
http://savemisterrogers.com/
http://www.leadingtoday.org/
http://theskinnywebsite.com/site/
earfarm.com/features/daily-feature/monday/2010
http://www.esart.com/blog/
http://electronicexplorations.org/the-show/week-047-drumcorps/
http://www.dailywireless.org/2009/02/06/2009-mobile-world-congress/
http://privacycouncil.org/
http://www.greenmamma.org/blog/
http://www.lunch20.com/2007/04/27/lunch-20-linkedin/
http://evil-e.org/
http://www.drdzoe.com/
http://iohanet.org/
http://electricbeach.org/?p=147
http://www.therightperspective.org/2009/01/05/mallgate-broadsides-clintons/
http://www.durf.org/
http://feministlawprofessors.com/?p=8389
http://www.pcs.org/win-big-at-this-years-gala-bright-lights-havana-nights/
http://www.lunch20.com/2007/09/12/lunch-20-oracle/
http://www.thecriticalcondition.com/2009/02/17/when-reality-shows-approach-reality/
http://www.bigdbahead.com/?p=672
http://metroriderla.com/2009/01/01/2009-the-year-in-transit/
http://eyeonwilliamson.org/?p=4065
http://www.imprintsjournal.com/
http://www.casavaria.com/cafesentido/2008/12/25/980/doctors-without-borders-lists-top-ten-humanitarian-crises-at-end-of-2008/
http://www.nickhodge.com/blog/archives/2150