Relatively little is known about the Malon; there has been no formal contact with the Malon government as such, merely a series of accidental encounters with their ships. Since these encounters have occurred over thirty thousand light years apart, it is possible that Malon territory extends across these kinds of distances - making their space far larger than the Federation. However, the Malon are known to have access to at least one stable "spatial vortex" - apparently a form of wormhole. It is possible that they have access to others which allow them to cross large distances, or even that are able to build such phenomena themselves. At this point in time we simply do not know.
At least some aspects of Malon technology produce large amounts of Theta radiation, and the Malon dispose of this by dumping it in unpopulated areas of space. The amounts involved are such that this has caused significant levels of pollution, endangering several species. It is the freighters involved in this operation that the USS Voyager has encountered. On their first meeting in early 2375, Voyager offered the Malon technology which would eliminate their Theta radiation problems. unfortunately the Malon still appear to operate a profit based economy; since the waste dumping business would be totally destroyed by such technology, the Malon crews have been less than receptive to this idea. Several weeks later a Malon freighter attempted to steal an advanced probe belonging to Voyager, prompting the Starfleet crew to build the Delta Flyer to retrieve the probe first.
Later in the same year, Voyager encountered an abandoned freighter and recovered two crew members from nearby escape pods. This encounter allowed the crew to learn much more about the Malon. The freighters can carry enormous amounts of the toxins, over twelve trillion isotons on a single vessel. Should such a ship be destroyed it would devastate everything within three light years of the explosion. Their freighter crews generally suffer serious cell damage from their exposure to the Theta radiation, which they call 'freighter blight'. The Malon use analeptic compound injections to counter the freighter blight, but while the treatment keeps them alive it does not prevent skin scarring.
A crew member will typically work six months of the year on a Malon freighter; the exposure so received is expected to cut his life in half. The 'core labourers' who work closest to the waste receive the greatest dosage; less than one third are expected to survive any given trip, but they make more money in two months of working than most Malon earn in a lifetime. Occasionally the radiation causes core labourers to experience mutations, and the Malon have many stories of 'monsters' which attack crew members or damage ships. Voyagers crew encountered one such individual on board the abandoned freighter and were forced to kill him in order to prevent the ship from being sabotaged.