Does VV at any point, either in or out of the three Zones of Thought book, give any details as to the nature of "Perversions"? In the second book Fire Upon the Deep, the "Straumli Perversion" destroys multiple civilizations in the High Beyond, but VV doesn't write much about the means of take over or the nature of the "Class 2 Perversion" itself. There are hints that the perversion might be a sapient computer program, but he also says that Class 2 Perversions are always "malevolent in nature" and to me that suggests that there is something more to it. I'm fascinated by this aspect of the story - it has a very Lovecraftian "ancient and terrible things" feel to it.
Basically, it is indeed a sapient computer program, one so immeasurably intelligent that it can easily and rapidly (within seconds) find ways to control and assimilate any conventional intelligence. The mechanisms of how this is done are not described because they're beyond our understanding. But it might start out like the movie "Ex Machina" describes, by manipulation.
A "Class 2 Perversion" seems to be a label to describe an intelligence of this degree motivated by conquest rather than cooperation - much like the the "hegemonizing swarms" mentioned in Iain Banks' Culture novels.
So it's not really Lovecraftian except perhaps in the sense of Clarke's third law: any sufficiently advanced and malevolent intelligence is indistinguishable from a Great Old One.
Full agreement with Michael's answer. I just want to add a few textual briefs I ran across in a recent reread that portray "Class 2 Perversion Modes" of action generally and the "Straumli Perversion" specifically.
In the prologue, the nascent blight;
"...ten seconds, more change than ten thousand years of human civilization. A billion trillion constructions, mold curling out of every wall, rebuilding what had been merely superhuman."
Here we have the construction of a transcendent network described as "mold" that may be nano construction, bio, or hybrid. The countermeasure that was smuggled out by the freighter also manifests as mold, though slower growing.
Later in part one, Ravna contemplates how some of the recorded perversions have manifested- networks made unusable, sapient inhabitants rendered mindless zombies, the planet covered in "replicant goo." Replicant goo seems to be a nano tech substance similar to what attacked and brought down Relay's automation. And as noted by Blueshell and Ravna, in the high Beyond people have synthetic immune systems which is just one, text noted avenue for direct biological control by an outside power.
Ravna states that powers are either
"occasionally helpful, but mostly ambivalent,"
and I think we can assume that a perversion is a power that is any attitude not covered by that statement.
As to its "Lovecraftian" nature, I think it is certainly so. Again the prologue talks about the cliche' of "The curse of the mummy's tomb," and I think that had Lovecraft had the technological singularity in his palette of overwhelming and dreadful colors, he would have used it (as have many writers in the past decade.