Was windows designed to be unsecure?

Yes. Microsoft makes its decisions for business rather than technological reasons. . In an attempt to win the browser wars they made several design decisions that have created serious security problems. The perfect example is bundling IE in the OS. Another is allowing ActiveX controls to run in the browser.

Microsoft strategy of interoperability between their programs along with feature creep of both the OS and at the application level is also a business decision that has created big security holes.

Finally, to restate my original point and the root of the reason why linux is more secure- Linux and before it Unix were designed to be multi-user machines running in a networked environment, while Windows was not.