Horizon3 has raised $250 million in a Series E funding round, tripling the firm’s valuation from $650 million to $2 billion in the year from June 2025. The new funding was co-led by existing investors NightDragon and NEA, with participation from seven new investors and five returning backers.
These are the facts. The details provide a code for the confidence that VCs and private investors have in a firm. A key number in this code is the valuation. It sounds important – and it is – but it is somewhat tenuous, being based on assumptions rather than fact. It is based on financiers’ belief in the firm concerned.
That belief comes from the firm’s past performance, the size of market it serves, and assumptions that both performance and market will continue to grow.
Horizon3 was founded in 2019. Its founders had concluded, explains the firm’s chief revenue officer, Matt Hartley, “AI will allow attacks at a speed and scale that will render human-centric defenses inadequate – cybersecurity will inevitably evolve into machines fighting machines at machine speed.”
Since every firm in the world requires cybersecurity defenses, and – at that time – most were human-centric and potentially obsolete, Horizon3 had identified a massive market and proceeded to develop a machine solution to the machine threat: the use of AI to tackle the growing AI threat.
