In the last few days I have noticed that something is slowing up my computer quite significantly in the period about 2-5 minutes after boot-up, or possibly 2-5 minutes after first connecting to the internet (which is the usually the same thing). Looking at the Task Manager, CPU usage seems to be peaking at 100% occasionally during this time, but I can't see any unusual programs or processes causing this.
I usually run Live Update first (manually) when connecting to the internet, and then open Thunderbird or my browser, and these have been taking longer to open than previously, and slow to respond when I start using them, eg scroll bars don't move instantly etc. After about 5 minutes, everything seems to be normal again.
I am using Windows 7 HP 64-bit, and two things changed just before this problem started: I upgraded from NIS 2010 to 2011 (18.5.0.125) which had downloaded itself automatically; and I got the standard Windows updates issued on 11 Jan (KB2419640, KB2454826, KB8890830 & KB976902).
Is the slowing up likely to be the result of NIS 2011 doing things a bit differently from 2010, so that more is going on in those first 5 minutes? Or is there something amiss that I need to be worried about? I don't think it's any kind of malware, since NIS scans are clean and it seems to only happen in the first 5 minutes, so I'm more concerned that it's some kind of program bug.
Thanks for any ideas.