Hackers vs Cloud computing

[Lamplighter]

"Cloud computing" seems to be the latest direction of business software,
and since I really don't know what it is, it sounds like the "big computer in the sky".
But that's being sarcastic and it's not my intention here.

If businesses do shift over to "cloud" environments, is there significant worry about the impact of "hackers" ?

My naivete makes me assume that hacker attacks,
such as the recent Denial of Service (DDoS?) war on MasterCharge, PayPal, etc.,
could just well be on whatever business system is using the "Cloud" environment.

Is that the case ? If so, why would business elect to go that direction ?