SOMEWHERE ON THE EASTERN SEABOARD – Prisons are easier to enter than Visa's top-secret Operations Center East, its biggest, newest and most advanced U.S. data center.

The 8-acre facility looks like any other industrial park in a sleepy suburb. But the serene setting masks hundreds of cameras and a crack team of former military personnel. Hydraulic bollards beneath the road leading to the OCE can be quickly raised to stop an intruding car going 50 mph. Any speed faster, and the car can't navigate a hairpin turn, sending it into a drainage pond that functions as a modern-day moat.

The data center resembles a fortress, with dogged attention to detail. It can withstand earthquakes and hurricane-force winds of up to 170 mph. A 1.5-million-gallon storage tank cools the system. Diesel generators onsite have enough power, in the event of an outage, to keep the center running for nine days. They generate enough electricity for 25,000 households.

Once you get clearance from a guard station, get an OK from a roving security guy in a golf cart, and surrender a photo and fingerprint inside, the adventure begins.

There are plenty of reasons for the airtight security. Billions, in fact.

In an era when mobile purchases on smartphones and tablets are expected to grow 73% to $11.6 billion in the U.S. this year, security is a necessary obsession at OCE — and an acknowledgment of the perils posed by profit-minded hackers.

Mobile payments are just a trickle of the more than 200 million daily transactions processed here and at one other Visa data center in North America.

"We're at the forefront of data centers," says Rick Knight, head of global systems operations and engineering. "Now everyone has to do it."

The fortress is home to the facility's 130 workers, who are entrusted with the arduous task of keeping hackers out and the network up.

OCE is a "Tier 4" center, a certification from data center research organization Uptime Institute that requires that every mainframe, air conditioner and battery have a backup.

To meet such lofty standards, Visa has poured hundreds of millions of dollars annually into developing state-of-the-art risk-management technology. VisaNet's services include transaction risk scoring, data encryption and transaction alerts. It all adds up to highly accurate models to identify and address potential fraudulent deals before they're concluded. That has contributed in great part to global fraud rates of just 6 cents per $100 spent, according to Visa.

Visa's core-transaction network is private, immune — the company says — from Internet dangers such as denial-of-service attacks by the likes of Anonymous. When hackers took down Visa's corporate website in 2010, for example, it had no impact on the core network.

Data about data centers

More than half of the world's 13,000 large data centers are in the U.S., according to market researcher Gartner. It estimates $22 billion will be spent on new centers worldwide this year, after growth sputtered during the recession.

Data centers are increasingly in vogue as demand for digital data explodes with the popularity of cloud computing, tablets and smartphones. Google, Facebook and Apple are among the large tech companies that built their data centers in rural areas to save on land and power.

"Physical security is the foundation where you start," says John Thielens, chief security officer of Axway, a business-software vendor. "If you can afford it, build a data center. The big guys build their own."

At the same time, Hewlett-Packard, IBM and others have plunged into the business of managing data centers for corporate clients, says Philip Russom, a research director for The Data Warehousing Institute. Amazon.com says it offers cloud-based "data centers for rent."

"The growth in data center construction is very much tied to the growth in the amount of data which needs to be stored and delivered to businesses and consumers," says Rakesh Shah, director of product marketing and strategy at data-security firm Arbor Networks.

Visa is loath to say how much it spent to build its data center, but a conservative estimate is probably hundreds of millions of dollars, based on construction costs and equipment housed at the facility.

Once inside, visitors encounter a "mantrap" portal, which requires a badge and biometric image of the right index finger to gain access to the data center. The digital image is necessary to pass through a phalanx of shatter-resistant glass doors.

A NASA-like command center, with a 40x20-foot wall of screens and 42 firewalls, monitors the company's worldwide network, which Visa says processes 2,500 transactions per second.

Inside the fortress

The data center's main corridor is about three football fields long, connecting seven 20,000-square-foot rooms called pods.

Two pods contain Visa's core network, a third its corporate networks, and the fourth, development work. A fifth pod handles Visa's new mobile platforms, such as the recently acquired Fundamo, a mobile financial services platform. Two dormant pods await expansion.

Pods 4 and 5 are the brains of the network, a blur of hard drives spinning and fans whirring amid rows of IBM mainframes, Cisco Systems switches and EMC and Hitachi storage arrays. They're all connected by 3,000 miles of cable — enough to traverse the country.

"Yeah, this place is pretty impressive, but there's a lot at stake (in terms of security)," Knight says. "We need to keep things safe."