jQuery checkbox change and click event

Demo

Use mousedown

$('#checkbox1').mousedown(function() {
    if (!$(this).is(':checked')) {
        this.checked = confirm("Are you sure?");
        $(this).trigger("change");
    }
});

Most of the answers won't catch it (presumably) if you use <label for="cbId">cb name</label>. This means when you click the label it will check the box instead of directly clicking on the checkbox. (Not exactly the question, but various search results tend to come here)

<div id="OuterDivOrBody">
    <input type="checkbox" id="checkbox1" />
    <label for="checkbox1">Checkbox label</label>
    <br />
    <br />
    The confirm result:
    <input type="text" id="textbox1" />
</div>

In which case you could use:

Earlier versions of jQuery:

$('#OuterDivOrBody').delegate('#checkbox1', 'change', function () {
    // From the other examples
    if (!this.checked) {
        var sure = confirm("Are you sure?");
        this.checked = !sure;
        $('#textbox1').val(sure.toString());
    }
});

JSFiddle example with jQuery 1.6.4

jQuery 1.7+

$('#checkbox1').on('change', function() { 
    // From the other examples
    if (!this.checked) {
        var sure = confirm("Are you sure?");
        this.checked = !sure;
        $('#textbox1').val(sure.toString());
    }
});

JSFiddle example with the latest jQuery 2.x

• Added jsfiddle examples and the html with the clickable checkbox label

Tested in JSFiddle and does what you're asking for.This approach has the added benefit of firing when a label associated with a checkbox is clicked.

Updated Answer:

$(document).ready(function() {
    //set initial state.
    $('#textbox1').val(this.checked);

    $('#checkbox1').change(function() {
        if(this.checked) {
            var returnVal = confirm("Are you sure?");
            $(this).prop("checked", returnVal);
        }
        $('#textbox1').val(this.checked);        
    });
});

Original Answer:

$(document).ready(function() {
    //set initial state.
    $('#textbox1').val($(this).is(':checked'));

    $('#checkbox1').change(function() {
        if($(this).is(":checked")) {
            var returnVal = confirm("Are you sure?");
            $(this).attr("checked", returnVal);
        }
        $('#textbox1').val($(this).is(':checked'));        
    });
});