I've done a major update of my browser, which seems to have dealt with all the problems. I did say that I don't do internet banking and I'm NOT going to wipe my pc. Thanks for the advice, but I think it's a bit alarmist under the circumstances. The only time I've wiped a pc has been when the hard-drive completely failed. I also had to buy a new laptop. I don't connect to the internet on the old pc anymore, just use it for designing posters (it has a better screen ratio) and playing games.
BTW the only warnings I'm getting from the trial of Malwarebytes that they've blocked malware is when I connect to MR.
