It is illegal for you to scan a Bank's computer but, they can , at least according to Halifax. When you visit the Halifax login page, even before you've logged in, JavaScript on the site, running in the browser, attempts to scan for open ports on your local computer

Halifax explicitly says they'll run software to detect malware... but that's if you're a customer. Halifax currently scan everyone, as soon as you land on their site.


Moore said he wouldn't have an issue if Halifax carried out the security checks on people's computers after they had logged on. It's the lack of consent and the scanning of any visitor that bothers him. "If they ran the script after you've logged in... they'd end up with the same end result, but they wouldn't be scanning visitors, only customers," Moore said.

https://www.theregister.co.uk/2018/08/07/halifax_bank_ports_scans/