The price of being popular…
When software is popular, then there are elements out there who seek to profit from it by less ethical means. Installer packages with added spyware, adware or even malware are apparently part of the (Windows) user experience these days.
GIMP is being attacked in that manner as well, In order to keep safe, get GIMP from our own downloads pages or the sites we link to, and be very cautious when going elsewhere.
One victim of this is GIMPshop – started as a fork of GIMP to add UI terms that are more familiar to users of Adobe Photoshop, it is nowadays used to load third-party software onto the unwary user’s system. Thankfully, the original author is not to blame, as this operation is run by someone else.