Security isn't just about protecting your identity and financial information, although those are important. It is also key to preserving the integrity of and access to your data and applications in the cloud. Things like firewalls, encryption, backups, isolation of resources, the strength of authorization at user interfaces and screening of employees and other customers can determine who can get to your resources, how they can do so and what they can do with them.
There are many disruptive things that a malicious intruder can do. A denial of service attack, which involves bombarding a system to the point where it is inaccessible for normal usage, can render your cloud services temporarily unavailable. A hijacked account could lead to your data or business transactions being redirected for ill purposes, or loss of access to your own services. A compromised system could allow a virtual machine housing your applications and information to be migrated to a malicious server, leading to exposure of information and possible loss of data. Malicious software (malware) can infect the system and disrupt operations, or even compromise your home or work computer if it spreads.Even if an attack doesn't cause you to lose data or access, any security breach will likely lower your comfort level with storing or retrieving information from the cloud.
Unfortunately, there are no entirely unbreachable systems. Anything accessible via the Internet is vulnerable. But the tougher a cloud provider's security and the better its ability to detect and recover from breaches, the less likely you'll be to lose access, data or peace of mind.
And security is not all up to the cloud host. Personal lapses, such as succumbing to a phishing scam (where you are tricked into giving away login credentials) or downloading malware from another source can have consequences for your cloud access as well. Vigilance is required on all sides.