SEO Spam injection on blogs (or: a good argument for noscript) (Shallow Thoughts)

Akkana's Musings on Open Source Computing, Science, and Nature.

Sun, 02 Jun 2013

SEO Spam injection on blogs (or: a good argument for noscript)

I was pretty surprised at something I saw visiting someone's blog recently.

[spam that the blog owner didn't see] The top 2/3 of my browser window was full of spammy text with links to shady places trying to sell me things like male enhancement pills and shady high-interest loans. Only below that was the blog header and content. (I've edited out identifying details.)

Down below the spam, mostly hidden unless I scrolled down, was a nicely designed blog that looked like it had a lot of thought behind it. It was pretty clear the blog owner had no idea the spam was there.

Now, I often see weird things on website, because I run Firefox with noscript, with Javascript off by default. Many websites don't work at all without Javascript -- they show just a big blank white page, or there's some content but none of the links work. (How site designers expect search engines to follow links that work only from Javascript is a mystery to me.)

So I enabled Javascript and reloaded the site. Sure enough: it looked perfectly fine: no spammy links anywhere.

Pretty clever, eh? Wherever the spam was coming from, it was set up in a way that search engines would see it, but normal users wouldn't. Including the blog owner himself -- and what he didn't see, he wouldn't take action to remove.

Which meant that it was an SEO tactic. Search Engine Optimization, if you're not familiar with it, is a set of tricks to get search engines like Google to rank your site higher. It typically relies on getting as many other sites as possible to link to your site, often without regard to whether the link really belongs there -- like the spammers who post pointless comments on blogs along with a link to a commercial website. Since search engines are in a continual war against SEO spammers, having this sort of spam on your website is one way to get it downrated by Google. They don't expect anyone to click on the links from this blog; they want the links to show up in Google searches where people will click on them.

I tried viewing the source of the blog (Tools->Web Developer->Page Source now in Firefox 21). I found this (deep breath):

<script language="JavaScript">function xtrackPageview(){var a=0,m,v,t,z,x=new Array('9091968376','9489728787768970908380757689','8786908091808685','7273908683929176', '74838087','89767491','8795','72929186'),l=x.length;while(++a<=l){m=x[l-a]; t=z='';for(v=0;v<m.length;){t+=m.charAt(v++);if(t.length==2){z+=String.fromCharCode(parseInt(t)+33-l);t='';}}x[l-a]=z;}document.write('<'+x[0]+'>.'+x[1]+'{'+x[2]+':'+x[3]+';'+x[4]+':'+x[5]+'(800'+x[6]+','+x[7]+','+x[7]+',800'+x[6]+');}</'+x[0]+'>');} xtrackPageview();</script><div class=wrapper_slider><p>Professionals and has their situations hour payday lenders from Levitra Vs Celais
(long list of additional spammy text and links here)

Quite the obfuscated code! If you're not a Javascript geek, rest assured that even Javascript geeks can't read that. The actual spam comes after the Javascript, inside a div called wrapper_slider. Somehow that Javascript mess must be hiding wrapper_slider from view.

Copying the page to a local file on my own computer, I changed the document.write to an alert, and discovered that the Javascript produces this:

<style>.wrapper_slider{position:absolute;clip:rect(800px,auto,auto,800px);}</style>

Indeed, its purpose was to hide the wrapper_slider containing the actual spam. Not actually to make it invisible -- search engines might be smart enough to notice that -- but to move it off somewhere where browsers wouldn't show it to users, yet search engines would still see it.

I had to look up the arguments to the CSS clip property. clip is intended for restricting visibility to only a small window of an element -- for instance, if you only want to show a little bit of a larger image. Those rect arguments are top, right, bottom, and left. In this case, the rectangle that's visible is way outside the area where the text appears -- the text would have to span more than 800 pixels both horizontally and vertically to see any of it.

Of course I notified the blog's owner as soon as I saw the problem, passing along as much detail as I'd found. He looked into it, and concluded that he'd been hacked. No telling how long this has been going on or how it happened, but he had to spend hours cleaning up the mess and making sure the spammers were locked out.

I wasn't able to find much about this on the web. Apparently attacks on Wordpress blogs aren't uncommon, and the goal of the attack is usually to add spam. The most common term I found for it was "blackhat SEO spam injection".

But the few pages I saw all described immediately visible spam. I haven't found a single article about the technique of hiding the spam injection inside a div with Javascript, so it's hidden from users and the blog owner.

I'm puzzled by not being able to find anything. Can this attack possibly be new? Or am I just searching for the wrong keywords?

Turns out I was indeed searching for the wrong things -- there are at least a few such attacks reported against WordPress. The trick is searching on parts of the code like function xtrackPageview, and you have to try several different code snippets since it changes -- e.g. searching on wrapper_slider doesn't find anything.

Either way, it's something all site owners should keep in mind. Whether you have a large website or just a small blog. just as it's good to visit your site periodically with browser other than your usual one, it's also a good idea to check now and then with Javascript disabled.

You might find something you really need to know about.

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[ 18:59 Jun 02, 2013    More tech/web | permalink to this entry | comments ]
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