My friend's daughter's laptop has a funny (I think dangerous) problem after the "Internet Security" warning pops up for a while and ask her download something. She didn't do that.

Later on this pop up does not display anymore but her computer react strangely. For example, if she dbl click on the short cut to Words, she has "Application not found" error; but she can dbl click a doc file and open the Words. If she dbl click on Internet Explorer short cut, an Open With dialog box comes up, we choose the Internet Explorer, the IE flashes and change to the Windows Explorer. I open the Control Panel and run Add & Remove program or User Accounts, I got the Application not found error for the rundll32.exe. I Run the msconfig or regedit, the Open with dialog box display again.

If I log in as Guest, I can run regedit (not msconfig which required Admin rights), open IE without go to the Windows Explorer, but when I dbl click on Words, the windows installer kicks in to install (the SW was completely installed long time ago). Then an error 25090 display but after clicking the OK button, the Words did open.

She did the virus scan by AVG and the computer looks clean. What is the problem and how can I resolve it? Thanks for your advices.