Cloud computing has a lot of business benefits, such as cost effective, flexible and a fast time to deploy. But there are also at least 5 major risks any business should try to mitigate before using a ‘public’ cloud service.
Risk 1: Vendor Lock-In
Will your organization be able to migrate “cost & time effective” to another cloud service ?
Most cloud providers benefit intentionally or unintentionally from 
keeping things proprietary as long as possible. Providers can also suddenly announce cost increase or be bought out by a larger company resulting in policy and or location changes.
Therefore your organization should define a clear exit strategy and include the ‘exit’ costs into the initial cost analysis.
Risk 2: Insecure of incomplete data deletion
Will your cloud provider be able to delete your data securely on your request ?
Cloud providers store your data safely by making multiple copies. The data is stored on multiple disks that are shared with and reused for other customers. So they cannot simply shred the hard disks. A request to delete data, as with most operating systems, may also not result in true wiping of the data.
If a Cloud provider does not (securely) delete data before reassigning space, leaking personal or strict confidential data of your organization especially in case of multiple tenancies could represent a high risk.
Risk 3: Loss of governance
Is your business still in control over the availability, performance, data integrity, resolution times of incidents and problems if the outsourced service is delivered by a Cloud provider?
Most cloud services have pre-defined service levels and do not offer negotiated Cloud Service Level Agreements. However to stay in control during 
contract negotiation at least the following important criteria needs to be agreed: availability (e.g. 99.99% during work days), performance (e.g. maximum response times), portability of the data (e.g. ability to move data to another provider) and resolution times of incidents.
As a cloud consumer you need to be sufficiently in control of your IT systems. For more help click here.
Risk 4: Loss of control on your encrypted data
Who really owns your data if you as customer do not own the encryption key?
While a cloud provider may agree to keep the data confidential (i.e., they 
won’t show it to anyone else) that promise does not prevent their own exploitation of the customer data e.g. to improve search results, to deliver ads or to mine data for their own purpose . Also, If the user encrypts the data, it’s more difficult for the cloud provider to deliver some cloud services (e.g. search).
However the fact that you are not in control of the keys to encrypt or decrypt your own data is a substantial risk that companies should try to avoid.
Risk 5: Insecure virtualization layer
How secure is the virtualization layer used by your Cloud provider?
Most cloud providers use virtualization– inside physical device virtual 
systems are built. This virtualization enables the provider to use physical devices in a more economic way. However virtual firewall support that exists today is very limited and attackers learned how to compromise the virtualization layer to gain control of the operating systems on virtual machines.
A compromise like this could give attackers complete control of your data. Together with your Cloud provider, organizations should agree on measures to mitigate this major risk.
John Bun 