Windows Update decided that I needed update KB955430, so it installed it. This was 4 days after I'd installed MSE (which was working fine). After a reboot the computer would freeze (solid) not on the connecting to the internet (dialup) but when starting any program to access the internet (email, chat, browser). The first couple times it did this I picked a restore point prior to the KB955430 install, and everything was good. Then the computer decided to have a crash (reason unknown) and not only was this update installed, all my prior restore points were lost. I ran sfc /scannow & found a hash missmatch for a single file 'wdma_usb.inf_loc' that couldn't be corrected as it says that both the file & backup file were corrupted. (Am using a file from an update in 2008 - it's comparing it to a file from 2006).
Yesterday ran eventvwr.msc and found that when my machine starts I have a 'image hash not valid' for 3 different files - one instance each of
\device\harddiskVolume2\windows\system32\drivers\S SPORT.SYS & DGIVECP.SYS and 12 instances of
\device\harddiskVolume2\program files\microsoft security essentials\drivers\mpfilter\MPFILTER.SYS.
So, I uninstalled MSE. Computer is again happily online and I've now got a few more grey hairs.