Q: What is Spug download?

It appears to be a text file associated with some Torrent software based on a brief Google search.

If you are using torrent software, it is ill advised.   The best places to get Mac software include the Apple App Store, the individual software developers, and http://www.macupdate.com/

Some other download sites may appear on http://www.macsurfer.com/ from time to time.

Although you should ignore advertising for MacKeeper that many Mac software download sites refer to.   This is as much a malware as Torrent software.  Many people who use peer2peer software to get their software should consider instead http://www.sourceforge.net for open source software if they can't afford high end commercial software.    First off, peer2peer software frequently pushes software your way without your acknowledgement, and frequently gives you versions that are laden with malware or are guinea pig test software that may be labelled final release but aren't, and if they do use your machine as a server can slow down your internet.  Not to mention if it is commercial software whose license key given without payment, that is illegal, and we can't discuss such activities on this forum.