Hook into the plugin update process of WordPress part I

function auv_check_for_updates( $transient ){
    if ( empty( $transient->checked ) ) {
            return $transient;
    }

    //Get the current version available
    $url = 'http://websupporter.net/current-version.txt';
    $response = wp_remote_get( $url );
    $version = (float) $response['body'];

    //Get information about the installed version
    if( ! function_exists( 'get_plugin_data' ) )
        require_once( ABSPATH . 'wp-admin/includes/plugin.php' );

    $plugin_data = get_plugin_data( __FILE__, false, false );

    //If update is needed
    if( version_compare( $version, $plugin_data['Version'], '>' ) ){

        //add our information
        $update_info = array(
            'plugin'        => plugin_basename( __FILE__ ),
            'slug'          => plugin_basename( __FILE__ ),
            'new_version'   => $version,
            'url'           => 'http://websupporter.net/',
            'package'       => 'http://websupporter.net/current-version.zip',
        );
        $transient->response[ plugin_basename( __FILE__ ) ] = (object) $update_info;

    }
    return $transient;
}
add_action( 'pre_set_site_transient_update_plugins', 'auv_check_for_updates' );