Submitter's note: Gimp is actively being maintained and the definition of "mirror" is quite misleading here as a modified binary is no longer a verbatim copy. Download statistics for Gimp on Windows show SourceForge as offering over 1,000 downloads per day of the Gimp software.
In an official response to this incident, the official Gimp project team reminds users to use official download methods. Slashdotters may remember the last time news like this surfaced (2013) when the Gimp team decided to move downloads from SourceForge to their own FTP service. "Therefore, we remind you again that GIMP only provides builds for Windows via its official Downloads page." Note: SourceForge and Slashdot share a corporate parent. Editor's note: I just got back from a busy weekend to see that a bunch of people are freaking out that we're "burying" this story, so here it is. Go hog wild. Sorry it took so long. (And for future reference, user submissions are easily found in the firehose, listed in the order they appear, newest first.)
Update: 06/01 22:37 GMT by T : The SourceForge blog has a welcome update; SourceForge, it says, has effective today "stopped presenting third party offers for unmaintained SourceForge projects. ... At this time, we present third party offers only with a few projects where it is explicitly approved by the project developer, or if the project is already bundling third party offers."