I don't remeber where I got it from, but a possible source is:Sharetastic - GoForSharing

It's most probably based on the shareaza code.

As to malware, its documentation states explicitly: "NOTE: Sharetastic does NOT include spyware and adware!".

So, the puzzle stays unsolved. I have very good experience with shareaza and keep using it, but, still, am puzzled about this newly made kin.