One feature that gets requested a lot is to be able to set a variable in the URL that could then be attached to the visitor as custom data. This would be particularly useful for things like email newsletters, so when someone clicks through, they can be identified automatically.

The variable name needed to be generic because of our white label program, and since we pictured this being used with “campaign activity” more than anything else, we decided to call the variable utm_custom (related to Google/Urchin’s utm_campaign etc variables).

You can see full documentation here. Because custom data requires a Pro or higher account (upgrade), this variable will also only be processed if you have a Pro or higher account.

utm_custom is an associative array so you can set multiple key/value pairs on a single page. (It must be an array with at least one key/value pair, or it will be ignored). For example, if you sent a visitor to this page:[username]=Bob+Jones&utm_custom[email][email protected]

You would see this in your visitor’s list:

And this when viewing visitor/session details:

We’ve had requests for this countless times over the years so we know many of you will find it quite useful 😀