File permissions got modified - liveupdate and windows update used regularly - passed full scan

Hi,

 

  In my computer windows and symantec was up to date. I connected to a friend's computer and copied some files to his share. But, he does not updates windows and anti virus (for months) on many computers on his network. I also installed bluetooth and wireless drivers at his place.

 

When I came back, I connected an external hard disk to my laptop and accessed some files on the external disk. But after a few I found that for some files in the external hard disk (especially those that I recently accessed) - their file permissions were removed. After doing some research, i found how deal with permissions. Then i realized that inheritable permissions on those files were deleted - and following two permissions were added instead: 1 administrators group - full control 2 system user full control. Even the ownership was also taken from me and given to the Administrators group. I fixed some of the files by clicking include inheritable permissions for them.

 

Then I ran a full scan (for 5-6 hours, and before that I executed live update successfully), and full scan found nothing. I did not find any new startup program. The network activity in symantec does not show any suspicious program connected to network whenever i check it occasionally.

 

Can I be infected with malware.

 

Any help or suggestion will be appreciated - I need to perform transactions related to bank account and I am getting nervous about doing them.

 

regards,

sukhwinder.