You shouldn't ever directly include data that is provided by a user in your SQL. It should always be bound, or quoted where binding isn't available. 
# Interpolated ... bad
my $sql = "insert into hits (browser) values ('$ENV{HTTP_USER_AGENT}')
+"
$dbh->do($sql);

# Bound ... best

my $sql = "insert into hits (browser) values (?)";
$dbh->do($sql, {}, $ENV{HTTP_USER_AGENT});

# Quoted ... tolerable
my $sql = sprintf "insert into hits (browser) values (%s)", $dbh->quot
+e($ENV{HTTP_USER_AGENT});
$dbh->do($sql);

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It is trivial for users to modify their user agent string, never trust users.

In reply to Re^5: Making a regex case insensitive by imp
in thread Making a regex case insensitive by Win

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