Spam Tracking Techniques
This article is about how spammers tracks who actually click on links in spam. An alternative name for this article would be “Never Click on Links in Spam”.
We all know that spam is cheap to send. But spammers know that there actually is a cost involved and they want profit from sending them. Therefore information about who actually reads the spam and clicks on links is worth gold. Even if they don’t stop sending spam to anyone they will prioritize sending to those that are known to receive them. To gather this information there are a few techniques spammers use. The primary techniques are images and links.
Images are an easy way to track who views the mail. Spammers insert images into the spam and name the file with a unique name for each spam sent. When the mail is viewed the mail client loads the image and the spammer can see who actually opened the mail.
Links are used in a similar way but the information gathered by the spammer is even more valuable. Not only does this prove to the spammer that the recipient read the mail but that he or she is actually willing to act upon spam. This is just the kind of people that spammers want to send spam to.
But how can you give each recipient a unique image to download? It’s actually quite simple, you don’t. Instead you give each recipient a unique name for the same image. Independent of what filename you ask for, the web server responds with the same file. This is actually quite easy to do on most web servers. Another way is not having any image. The web server then logs the request as a 404, which means File Not Found. The spammer then analyses the logfile where all the information wanted can be found.
The good news is that some email clients, for example FireFox, by default does not show images. Instead you have to choose to show them, thereby protecting you from image tracking. Not clicking links in spam is, however, still something you need to learn.