How to get the Split value from collection?
Naming
I don't get the _ underscore prefix. This typically identifies a private field (albeit controversial). I'm pretty sure there's a consensus about simple camelCasing for local identifiers.
The name _websiteList is a bad one, for two reasons:

It's of type WebSiteAddress, which has words Web and Site; the name isn't following the established casing convention, should be _webSiteList.
It's tying the variable to its type. Would the name still make sense if the type was WebSiteAddress[]?

A better name would be, simply, webSiteAddresses.
Typing
If you want to use LINQ, you're targeting .NET 3.5+. Therefore, you can use implicit typing to improve the readability (and possibly the maintainability) of your code (although that's possibly personal preference).
Consider:

var webSiteData = _divider[1].Split('=');


The SO answer gives you a nice LINQ-oriented approach.