Avast doesn't like the latest TAudioConverter 0.9.9 download. while I recognize that this is, no doubt, a false positive, I wonder if it might be related to the crapware that SourceForge has take to adding to some downloads. Search on VLC or Gimp and SourceForge for details.
It's a false positive within Avast and only Avast. You can submit it to them so they can fix their error. Here's the Virus Total report as of 2 minutes ago:
https://www.virustotal.com/en/file/b6af4da110698a96170bcd79e91d8fffb29ff...
As per the other bit, SourceForge doesn't modify files or installers. At least they don't now and never have before. About 10 projects out of a couple hundred thousand on SF participate in SF's Dev Share program in which case a download stub installer is served instead of the real program's installer. It shows offers, downloads the real installer in the background, runs the real installer after the offer is shown, and SF and the project share revenue. It's an opt-in program that PortableApps.com doesn't participate in. Recently, for a short time, SourceForge was also serving this stub offer installer on a handful of mirror projects where SourceForge hosts the downloads for apps that don't host their binaries on SourceForge. After GIMP publicly objected to this practice and there was community backlash against it, this second program was halted about 2 weeks ago.
Currently, the only apps you'll find on SF with bundleware are apps like FileZilla and the handful of others that participate in SF's Dev Share program and other apps that do bundleware within their own installer that's completely unrelated to SourceForge (DVD Styler, CrystalDiskInfo, FreeFileSync, etc). Interestingly, SourceForge's bundleware is more easily discernable as an offer and more easily declined than the other bundleware included with other projects.
Sometimes, the impossible can become possible, if you're awesome!