Safe Mode Scan Reqires Admin Password?

I think my wife's Win7 PC may have a nasty since when it started it went to safe mode.  NIS11 is installed.  I started NIS and it asked if I wanted to do a full system scan.  It then asked for the administrator password.  Is this normal?  We have had no problems in the past doing a NIS scan when not in safe mode without being asked for administrator rights or password.