“SourceForge are (sic) abusing the trust that we and our users had put into their service in the past,” according to the GIMP project. Since 2013, SourceForge has been bundling junkware along with their installers — sometimes without a developer’s permission.
Don’t download software from SourceForge if you can help it. Many open-source projects now host their installers elsewhere, and the versions on SourceForge may include junkware. If you absolutely have to download something from SourceForge, be extra careful.