VMware shares fell 20 percent this morning on concerns that the cloud plans of enterprises are cutting into the company's business.

VMware's third-quarter earnings report yesterday beat expectations. But the company noted that third-quarter bookings — the deals that become revenues for future quarters — didn't produce the boost they normally do.

The company is predicting fourth-quarter revenues of $1.83 billion to $1.88 billion. Analysts were expecting $1.88 billion, according to Thomson Reuters, so the forecast counts as a disappointment.

At press time, VMware was trading down $13.76 (20%) at $55.

Executives on yesterday's earnings call blamed the macro-economy, as everyone does these days. They also noted the recent uncertainty around VMware's future. Before Dell made its $67 billion offer to acquire EMC, there had been speculation about whether EMC and VMware should separate, or whether VMware would even acquire EMC.

The big issue, though, was the "secular shift" among enterprise customers, as COO Carl Eschenbach politely put it. In other words, customers are considering new strategies built around clouds, and that's put a crimp in data center spending.

"Are they going to build a private cloud, are they going to build a public cloud, or are they going to leverage hybrid cloud services from someone like VMware or Virtustream?" Eschenbach said during the call. (As announced yesterday, Virtustream's cloud services are being merged with VMware's vCloud Air in a business to be jointly owned by VMware and EMC.)

"There's just a lot of uncertainty in our customers, and they're much more cautious when they think about engaging in a long-term contract with any technology vendor, I believe, not just VMware," Eschenbach said.

OpenStack is throwing a wrench into VMware's business as well. While customers could choose to use VMware Integrated OpenStack — VMware's own distribution of the open source platform — they've got plenty of non-VMware options to consider.

VMware didn't say this out loud, but: This adds up to a possible future where enterprises rely more on public clouds, possibly as part of a hybrid cloud strategy, and don't need as much of VMware as they used to.

However you paint it, the uncertainty over cloud strategies isn't going to end quickly, Eschenbach said. But he does think it's temporary.

"I think we're very well positioned, if people want to continue to build out private clouds. And I think we're uniquely positioned for customers who want to actually extend into public cloud, because no one house [owns] the hybrid capabilities that we have today," he said.

For its third quarter, which ended Sept. 30, VMware reported revenues of $1.67 billion and net income of $256 million, or 60 cents per share.

For the same quarter a year ago, VMware reported revenues of $1.51 billion and net income of $194 million, or 45 cents per share.

Non-GAAP net income of $1.02 beat the analyst consensus of $1, according to Thomson Reuters.

Quotes taken from the Seeking Alpha transcript of the earnings call.