Perl Security: 4. Handling tainted data
Detecting tainted data

It's  very easy to detect if a certain value is tainted or not: Remember that outside an eval, the program will not abort. Thus,

sub is_tainted {
    return ! eval {join ('',@_), kill 0;
    return 1;
}

We can also use the Taint module available at CPAN:
use Taint;
warn 'Tainted data!' if tainted ($var1, @var2);