I'd appreciate that, FJJP, because I seem to have this problem back too - and it seems to be PPRuNe related!
I've seen it in the past, but a live-update fixed it at some point. However, I was online last night and I noticed that something was eating all the available CPU - sure enough, it was the SymProxySvc process. I quit IE6 and killed the process, which instantly respawned but with the expected minimal CPU usage. All looked OK, so I started up IE6 and visited a couple of other sites. Still OK, but then I visited PPRuNe and - straight away - SymProxySvc CPU usage went up to 98% again. Quit/Kill - back to 1%. Go to The Register - 1%. Go to BBC News - 1%. Go to PPRuNe - 98%. Strange.
I didn't have time to look into things, so I'm not sure what was happening. I don't think that this has been happening ever since the great PPRuNe upgrade, so I suspect it happened when Norton live-updated a couple of days ago. However, I'm not sure why PPRuNe should trigger it.
I'm running XP/Pro, recent IE6 and a fully-updated Norton IS 2002. Ho hum...