A few links to read about the dangerous downloads being cancelled...

http://www.gnutellaforums.com/348490-post9.html

http://www.gnutellaforums.com/350144-post2.html

The latest Beta version (5.4.0) has the ability to check whether a file's dangerous before previewing - AFAIK no earlier versions could do this.

Don't forget to check files with Bitzi before download... if other users have rated the file then you'll get an idea of it's content & quality
How to use Bitzi