Filter special characters

[fadlisaad]

How do we block special characters from being sent? I've try and it was vulnerable to SQL injection.

Subject: Complaint from Yeap
To: [email protected]
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Date: Mon, 8 Dec 2014 17:16:44 +0800
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Internet slow <form method="post">
    <?php echo (Form::hidden('csrf', Security::token())); ?>
    <label><?php echo __('Name', 'contact'); ?></label>
    <input  type="text" name="contact_name" class="input-xlarge" value="<?php echo $name; ?>" /><br />
    <label><?php echo __('Email', 'contact'); ?></label>
    <input  type="text" name="contact_email" class="input-xlarge" value="<?php echo $email; ?>" /><br />
    <label><?php echo __('Message', 'contact'); ?></label>
    <textarea class="input-xxlarge" rows="10" name="contact_body"><?php echo $body; ?></textarea><br /><br />

    <?php if (Option::get('captcha_installed') == 'true') { ?>
    <label><?php echo __('Captcha', 'users'); ?></label>
    <input type="text" name="answer"><?php if (isset($errors['captcha_wrong'])) echo Html::nbsp(3).'<span class="error">'.$errors['captcha_wrong'].'</span>'; ?>
    <?php CryptCaptcha::draw(); ?>