Thanks to you too ukhardy07 & Tommy45 for the reassurance.
I had been a bit worried because I got an email from my ISP a few days ago telling me that my customer page was being accessed 30,000 times per month and using a bit of my bandwidth - whether that was an average based on a short time, I don't know yet. They may have the answer after the holidays and are monitoring the issue.
I've only been with them since Nov 17th, and the new router put in place on Dec 12th.
The customer page doesn't contain any sensitive information, so an odd thing to target.
Having run a number of scans, and assistance from Kaspersky UK, nothing amiss has been found, and my computer is working perfectly normally. The Kaspersky network monitor shows nothing untoward either.
The only problem I could think of was that the wireless was enabled on my new router for some days before I realised that I hadn't set any security on the wireless part of it. I disabled it as soon as I realised that.
I did think it was then pretty secure from outside access, but am glad to have the reassurances here