As outlined by Wikipedia, Cloud Security or alternatively Cloud computing security refers is the name given to a broad set of policies, controls, and technologies deployed to secure data, applications along with the connected infrastructure of cloud computing.

Cloud Security is a mutual responsibility
With the help of cloud computing and storage, users now have the ability to store and process their data in third-party data centres. Different firms and companies use the cloud in many diverse service models (e.g SaaS, IaaS, and PaaS) together with deployment models (public, private, hybrid, and community). The security of data available in the cloud is the concerns of both the Cloud providers (firms providing SaaS, PaaS or IaaS via the cloud) and the Customers (companies, firms or organizations whose application or data is stored in the cloud). This is a shared responsibility, in spite of this. The cloud service provider must make sure that their system is highly secured and their clients’ data and applications are secure and protected, at the same time the client absolutely will need to take precautions to fortify their application in addition to strong passwords and authentication measures.

Three of Kinds of Data Stored in the Cloud
When it comes to storing data in the cloud there are three kinds of data that can exist. Virtually every company has no less than two of the three, with a great number likely having all three:

- Public Data tends to be stored in the cloud with impunity. Basically, this data won’t be harmful to the company if publicly exposed and there are absolutely no regulations or control for this kind of information.
- Sensitive Data are pieces of information which can be stored in the cloud, however, are required to be secured somehow. The company might want this data to be encrypted just before storing it in the cloud.
- Restricted Data are information that simply cannot be stored in the cloud under any circumstances.

The Netwrix 2015 Cloud Security Survey discovered that 65% of companies have security worries when it comes to migrating to the cloud, while 40% are concerned about their loss of physical control over data in the cloud. Unfortunately, control does not necessarily imply security.

According to senior vice president of Cloud Technology Partners, David S. Linthicum, “systems built without the same rigour around security won’t be as secure, whether they are cloud or not. Here are guidelines for determining a well-defined security strategy:

1. Understand your security and governance requirement for a specific system and/or data store.
2. Understand that controlling access is much more important than the location of the data.
3. Finally, vulnerability testing is an absolute necessity, no matter if you’re testing the security of cloud-based or traditional systems. Untested systems are unsecured systems.

Knowing what the cloud is along with the kinds of data which really can be stored in the cloud is a key step to securing your company’s presence in the cloud. Not forgetting the fact that cloud security is the job for both provider and client.

Source: http://www.blog.descasio.com/things-you-need-to-know-about-cloud-security-today/

It's true that cloud security is a mutual responsibility, and I think entrepreneurs should keep that in mind because it happens pretty often when your data gets leaked or anything like that if you don't improve your office 365 data protection. It's actually important, and you need to consider it if you don't want to struggle with data leakage or anything like that.