If you're asking "is the cloud insecure by default", the answer is NO. Cloud is as secure as you make it. It is as secured or unsecured as your shared hosting, your VPS or your dedicated server.
Like the discussion in the other posts, cloud in itself does not mean anything different. It is the same underlying infrastructure that powers every other hosting type. The difference is just that there are multiple computers working behind the scene instead of one. Also, cloud does not mean that your data is accessible by default to everyone. No. Your data is accessible only by those your have granted permission to.