function validateContactForm() {
    /* Name */
    if (document.getElementById('txtName').value.length < 1) {
        alert("Please enter your name.");
        return false;
    }

    /* E-mail */
    var email = document.getElementById('txtEmail').value;
    if (email.length < 1) {
        alert("Please enter your email address");
        return false;
    } else {
        var isEmail = /^[_a-z0-9-]+(\.[_a-z0-9-]+)*(\+[_a-z0-9-]+)?@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,6})$/i.test(email);
        if (!isEmail) {
            alert("The format of your email address is not valid.");
            return false;
        }
    }

    /* Content */
    if (document.getElementById("txtContent").value.length < 1) {
        alert("Please enter your message.");
        return false;
    }

    /* CAPTCHA */
    if (document.getElementById("security_code").value.length < 1) {
        alert("Please enter the security code.");
        return false;
    }

    return true;
}