sub scan_installed {
    system ('reg query HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall /s > temp_instal.txt');
    
    open (INSTAL, "<", 'temp_instal.txt') or die "Couldn't open temp_instal.txt for reading: $!\n";
    while (<INSTAL>) {
        if (/DisplayName\s+REG_SZ\s+(.+)/) {
            push (@installed, $1."\n") unless $1 =~ /Windows XP|KB[0-90-90-9]/;
        }
    }
    close(INSTAL);
    system ('del temp_instal.txt');
}