William, a software developer just starting his career, was asked to create a website in PHP that would allow visitors to enter a month and a year for their birth date. The PHP code he creates has to validate the input after it is entered. If William uses the following code, what could a malicious user input to the year value to actually delete the whole website?

$month = $_GET['month'];

$year = $_GET['year'];

exec("cal $month $year", $result);

print "<PRE>";

foreach($result as $r)

{
print "$r<BR>";

}

print "</PRE>";