Thanks for your response.
I'm not sure I'd want to go through the trauma of re-installing Windows as I've got
lots of apps and the last time I performed a clean re-install, it took several weeks to get my system back the way I wanted it.
I've attached screen shots of part of my msconfig setup and you'll see that Sony PC Companion is listed twice in Startup (why?). It's also unchecked, so shouldn't run at startup, but after a while, if I open msconfig again, PC Companion will have become checked for some reason.
I've also disabled the PC Companion service, so I don't know what else to try, other than the suggested Windows re-install, which I'd rather not. Process Explorer does not reveal anything that is obviously suspicious, the only Sony items being Vaio processes for LAN, battery monitoring, etc.
Any more thoughts?