Hacking tools aren't illegal by default, that I know of anyway.
Also it seems like taking down the website stopped the software working. If it was centralised then there is a link between the theft of bank logins and the associated fraud directly to the website. Of course it might just be dialing in and checking the license as opposed to the website facilitating functionality.
Edit. Just seen an archived page for the tool, looks like a legitimate network access and monitoring tool. If that's the case then arresting the dev seems excessive. I did note that the page provided support, so I wonder if there was some entrapment along the lines of "how do I monitor for bank logins ?" Perhaps with enough info to make it clear the tool was being used to perform illegal activity, and that support is what fucked the dev?
A large portion of common law revolves around intent - I think the technical term is "mens rea" (mentioned by another poster).
If a site sold knives as "neighbor killers", with the comment "use this and you can definitely kill your neighbor, $19.95", then all the same considerations would come into play. And knives aren't illegal, at least to cook with.
It's a crime to own the software intending to use it even if you don't actually use it. Arguably, the purchaser intended to use it at the point they made the purchase; people don't typically purchase software like this accidentally (of course there are obvious exceptions like perhaps security researchers wanting to decompile it to understand how to block it in the future, etc.)
AFAIR that's different to how the act was prior to SCA2015. Indeed this section including "material kind" strongly suggests that the original intent was that the Act would punish material damage, rather than a trumped up suggestion by the CPS (on whomevers behalf) that an act might be reckless as to whether it creates an increased risk of serious damage.
This legislation seems to work like "well you went on a road near some property, which is exactly what a criminal who was going to destroy that property would do, so you're clearly guilty". It seems somewhat over-reaching to me.
However, they do have to actually take action and material damage is defined by s3ZA(2) with "damage to human welfare" (s3ZA(2)(a)) constrained by s3ZA(3).
It is unlikely that the threshold for a charge under S3ZA would be met. The more likely charge is S1 (unauthorised access) or S3A(3) which makes it an offence to obtain any article intending to use it to commit, or to assist in the commission of, an offence under section 1, 3 or 3ZA — you don't even have to actually use the software to be criminalised, merely possessing it is enough provided the prosecution can prove your intent beyond reasonable doubt.
You can read the Explanatory Notes for the SCA 2015 amendments that altered the CMA 1990 at http://www.legislation.gov.uk/ukpga/2015/9/notes/division/3/... for background on why these changes were made.
https://www.europol.europa.eu/newsroom/news/international-cr...
Presumably there would have to be some allegation of UK law-breaking in order to get a search warrant for properties in the UK.