When you purchase software from Information Builders, they will assign you a four digit customer number. Of course, IBI sold software to over 9,999 companies so they started using alphanumeric characters in that code. For example, you might get assigned something like 99AB.
In addition to your customer number, the IBI site code has a two-digit software license code. The four digit customer number is separated from the two-digit license code with a period. So if you own the FOCUS 4GL, the WebFOCUS enterprise BI product, and the iWay integration software, you might have three site codes like 99AB.01, 99AB.02, and 99AB.03.
If you make licensing changes (e.g., changing from lease to direct purchase), IBI might sunset your original site code (like 99AB.03) and give you something new (like 99AB.13). It is also not impossible to get a completely different customer code.
Using a site code, you can log into IBI's TechSupport site and download software updates. If you do not have a TechSupport account, all you need to activate one is your site code and the name of your company as described on the software license. Go to this link to setup a new user account.
Legend has it that since the start of the company IBI has been keeping these numbers in a 1970s ledger book. Personally, I picture the scene from the Mission Impossible movie where the US Embassy has a highly secure room for storing the NOC list, but perhaps IBI is not that fancy.
If you have any other questions, just let me know.