WP_Widget is deprecated bug report

If you are happy modifying php code then following code offers a quick fix. You will need the ‘mailchimp_widget.php’ file from the plugin folder. Then do the following:

Find the following function around line 483 up to 488:

function mailchimpSF_Widget() {
		$widget_ops = array(
			'description' => __('Displays a MailChimp Subscribe box', 'mailchimp_i18n')
		);
		$this->WP_Widget('mailchimpSF_widget', __('MailChimp Widget', 'mailchimp_i18n'), $widget_ops);
	}

and replace with:

function __construct() {
		$widget_ops = array(
			'description' => __('Displays a MailChimp Subscribe box', 'mailchimp_i18n')
		);
		parent::__construct('mailchimpSF_widget', __('MailChimp Widget', 'mailchimp_i18n'), $widget_ops);
	}

Reupload the file and the error should be gone.