The result of base64_decode that you are printing contains some control characters that are tricking the console into hiding some parts of the code. The actual result is this:
$_C0=base64_decode($_C0);$_C0=strtr($_C0,'(A.gPtO6r^MQ~§Y!,{3Lw0:Hq)ZWJ1dmDXn*
8`hfI-e´#4CNS2a5v[oi]kM;_xbjslcB^@u&7yzUT+p9>%G/F VK=}RE<','4AMK=/rOinY´_1
P~Bh:^Mx&Z5kTe*Dz]RVmLsUJIoX+FC)`NSW98(}2>vGE%f-QHb[uyg7ldq§,wj3<p0;#6{at.c !^@');$_R=str_replace('__FILE__',"'".$_F."'",$_C0);eval($_R);$_R=0;$_C0=0;
Which decodes into this:
if(time()>1359388391||time()<1359294791)die('<b>This script has been expired.</b><br />Scripts protected using the PHP Guard Trial Version are valid for 24 hours only.');?><?php
echo "Hello World!";
?><?php if(headers_sent())echo(base64_decode('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'));?>
Which decodes into this:
<div style='position:absolute;width:440px;left:50%;top:20px;margin-left:-250px;padding:8px;padding-left:49px;border:1px solid #999;background:#ff9 url(http://www.phpguard.net/script) no-repeat 26px 7px;font-family:Verdana,Geneva,sans-serif;font-size:12px;color:#666;' onclick='this.style.display="none";'>This script was protected using the <a href='http://www.phpguard.net' style='color:#06c;text-decoration:underline;font-weight:bold' target='_blank'>PHP Guard</a> Trial Version.</div>