When attempting to download the filezilla client the download redirects from sourceforge to ak.pipoffers.apnpartners.com which silently installs unwanted malware "hotspot shield".
This is not malware. Filezilla is participating in our DevShare program which we announced here: http://sourceforge.net/blog/today-we-offer-devshare-beta-a-sustainable-way-to-fund-open-source-software/
There is also a more recent update on this program, where we address some user concerns here: http://sourceforge.net/blog/advertising-bundling-community-and-criticism/
If you wish to follow-up on this issue, please use the appropriate resources as indicated in those blog posts.
Chris Tsai, SourceForge.net Support