Amazon has officially bought bankrupt ad tech firm Sizmek’s ad-serving technology, as was reported would happen a few weeks ago. The move is a sign of Amazon firmly digging its heels in and mounting a challenge to Google and Facebook’s advertising domination. Amazon has not announced how much it paid for Sizmek’s technology.

Alongside the purchase of the Sizmek Ad Server, Amazon has also acquired Sizmek Dynamic Creative Optimisation (DCO), which helps to personalise ads using data. Amazon says it was helped in its decision by its advertising unit, Amazon Advertising, having “many mutual customers” with Sizmek and knowing “how valued these proven solutions are to their customer base”.

At least for now, Sizmek Ad Server – which is used to manage and run ad campaigns across the internet – and Sizmek DCO will continue to operate separately from Amazon Advertising.

Sizmek filed for Chapter 11 bankruptcy in the US in March. Under the filing, it was revealed that that the company owed between 1,000 and 5,000 creditors money, while estimating its assets at between $100m and $500m.

The ad tech firm has already sold its demand side platform (DSP) and data management platform (DMP) to Zeta Global Holdings for around $36m.