The Install and Upgrade by Waindigo add-on checks all of a users add-ons to see if there are any updates available. For add-ons not listed for free on the Resource Manager, it works this out by checking the add-on ids against other people's add-ons they have installed (Waindigo and non-Waindigo).
For example, lets say you have Chris Deeming's Xen Product Manager add-on installed. When you update the add-on it notifies the Waindigo servers. Another site with this add-on then does its daily check for updates and receives a response to say that is an update available.
In order to provide this feature, the list of add-ons you have installed is sent to Waindigo servers.
The more people who use this add-on, the better it is for everyone.
There is nothing malicious about this.