What are Facebook Link Shims, and How Do They Affect Your Data?

If social traffic is important to your ecommerce store, you should be checking referral traffic stats in Google Analytics to see how many visits are coming from social media sites.  When it comes to breaking down Facebook, there’s a referral source that some marketers have found confusing. They are called ‘link shims’ and they show up like this:  

What are Link Shims?

The ‘l.facebook’ and ‘lm.facebook’ represent referrals that were directed through a link shim. The link shim was first introduced by Facebook in 2012 (you can read the Facebook post explaining the link shim here). However, it wasn’t until the spring of 2014 that it started showing up in referral reports.  Facebook implemented the link shim for two primary reasons:

1. To protect readers from malicious websites

If Facebook knows or suspects a link is spam or malicious, the link URL is rewritten to go through the link shim first. Facebook uses its own internal list of malicious links along with advanced machine learning classifiers to check website authenticity.

2. To protect users from unknowingly displaying personal information

Some URLs on Facebook contain private information, including vanity URLs that contain the name of the user. Without a link shim, the browser would send the URL to a third party site, revealing private information. Instead, Facebook uses the link shim’s address as the referrer.  

How to Interpret Link Shims:

The only official post about the link shim is from Facebook that we referred to earlier.   To help online businesses better understand how to interpret link shims, we did our own research and have come up with the following key takeaways:

 
• The link shim provides marketers with more visibility into social referral traffic. Prior to Google Analytics recognizing link shim Facebook referrals, the same sources would have been classified as none or unknown. That means more traffic that was originally from an unknown source will show up as Facebook traffic to give you a more accurate picture of your social referrals.

 
• The link shim was designed to hide personal information but retain the referral source. If you’re interpreting reports to understand how many referrals came from each social media site, you can count link shim Facebook traffic the same way you would direct Facebook traffic.

 
• Some website owners have expressed concern that their own website may be recognized as malicious by Facebook, prompting the link shim referral to appear. If your website is legitimate and safe, you have nothing to worry about.

 
• You may want to make a quick quality comparison of your direct Facebook referral traffic versus link shim referral traffic. You shouldn’t see much of a difference, however, a few website owners posting on forums have seen higher bounce rates and less time on their website by visitors who come through a link shim.

Ultimately, the link shim traffic should help ecommerce businesses make better marketing decisions based on a more accurate picture of social media referral traffic.  If you’re looking for other inside tips to get the most out of Google Analytics and marketing efforts, check out our posts on Link Tagging your Marketing Campaigns and the benefits of View Through Conversion Data.