Joomla 1 is it still safe to use?

If you use joomla 1 and no plugin can this one still get hacked? or is it still safe to use joomla 1 any thoughts? I have heard how older joomla can have big holes in them and you must upgrade is this because of holes in joomla or rather in templates and plugin created for joomla itself? Any help because joomla1 is lightweight and fast I was wondering to use it for a fats and un heavy alternative.... plus I like how it works better and more versatile than the future ones... If anyone has any thought or opinions on this please comment below I will be glad to hear from you as to whether I should use this version or not.. Or do you think that using a older version would be slower than using the newer ones?