The irony is that the risks are huge and more common than some, including a few posts here, will believe.
I have sat on the regional cyber security council run by the police commissioner (as for a while I was a NED of a cyber security firm who covers some Government contracts), and the issue is that businesses who are impacted keep it secret. Many don't even report it as they fear reputation damage, loss of confidence, etc.
As a company, if we ever experience a period longer than one hour of peace where there are no script kiddies or hackers attempting to infiltrate our online systems we do a check to make sure we're still online ?. It's permanent, literally never stops.
We are regularly targeted by Phishing emails, and even just yesterday my finance team received an email from my wife (!?!) asking for details of the closing bank balance. The LOL is that my investors insisted I sack her and remove her shares before they invested, she's barred from any involvement in the company ?? (investors don't like family businesses to invest in). They often get emails from "me" asking for payments to be made or bank info, is rife, and these people have tried impersonating everyone from our chairman, me, my wife and various colleagues.
We run regular Phishing tests across the company testing staff knowledge and training.
In the past a member of staff did receive an email from a customer asking them to check some details which resulted in an automated forwarder being added to their account that sent all emails containing the words payment or invoice to a gmail account.
I have two friends who's businesses were shut down for weeks by ransomware and all their data being encrypted, again by an email a member of the staff thought was from a colleague. These are small companies with less than a dozen staff.
I would argue the plumber example
@fisicx is the most vulnerable because they don't have the technical skills or support around them to put things in place, and they are a nice easy soft target. I've seen so much of it, heard so many horror stories, and my own business is under consistent barrage of it that many of our processes remain wet ink/paper based.