Thank you. Well spotted. I actually wasn't aware Trusteer was on this machine but must have installed it at some point on recommendation from Santander. Then when I searched for it, I realised the icon was glaring at me from the start up bar and I'd assumed it was something else. I have now removed it.
My husband has regularly warned me off anti-virus software so usually don't touch this stuff but obvs when your bank recommends it...and because it seems to be particularly bank security related and not 'anti-virus' as such it probably felt like something I ought to have. The article you posted is very clear and helpful. Plus, when I googled Trusteer to work out what it actually was, a Which? article appeared specifically warning people off it. And yet, people are less likely to read articles like this and more likely to, like me, blindingly trust their bank (which in an ideal world we should be able to). I have contacted Santander via Twitter to request they don't recommend it anymore, probably won't help, but can't hurt to try.