(FORTUNE Small Business) – Diane and Michael Bingham know how to manage a crisis. They weathered financial ruin when Diane, 39, needed the family's savings to put herself through alcohol rehab and again when Michael, 52, needed an emergency triple-bypass operation. Neither had health insurance. Just as the two had returned to solvency and were growing the online antiques firm they had founded (and that Diane runs), the most avoidable of crises struck: an e-mail virus.

The Klez e-mail worm invaded the Binghams' business, From Global to You, in 2002, flooding its in-boxes with e-mails and ultimately locking up its ten PCs. The damage shut down the business, based in Provo, Utah, for two days. It permanently lost about 30 customers fed up with the poor service and e-mail spam the virus caused. "The worst part is that our customers probably just thought we were being rude," says Diane. The company also lost about $7,500 in revenue from eBay auctions it couldn't complete before finding the security solution needed to start cleaning up the mess, one that delayed the firm's full expansion plans for almost two years.

The Binghams aren't alone. Between 35% and 40% of small to midsized businesses say they have been attacked by a virus or hacker, according to a recent study by tech-research firm Gartner. More alarming, half of those companies that say they've never been infiltrated probably have been but simply aren't aware of it. The MyDoom virus attacks so far this year are a fresh reminder of the havoc that can occur without adequate protection.

Diane Bingham thought she had taken the proper precautions to protect her computers before the attack, having spent several thousand dollars purchasing and installing various security programs, which in hindsight were misinstalled. Tech support was no help. (How's that for return on investment?) Her accountant recommended she switch to Invisus PC Security Solution, an upstart offering from another Provo company. Invisus, which now has a few thousand customers, sent technicians to the Binghams' warehouse to clean the infected PCs and install the new software. The Binghams were back in business $1,000 later--$100 per infected computer is the average cost of cleanup if there's been no data loss (the virus luckily didn't fry From Global to You's customer records). The Binghams pay $99 a year for each of their now 20 PCs to keep the software current. Competing products from industry titans McAfee and Norton start at $70 to $100 a PC annually.

The Invisus software, which includes a firewall and automatically updates both virus definitions and other programs, has let the Binghams focus on running their business and not worry about virus and hacker attacks. "If I can sit on the phone for 30 minutes trying to sell a $10,000 item instead of messing around with my computer, that's really valuable," Diane says. From Global to You has been able to expand internationally, regularly wiring close to $50,000 a month to its buyers in countries such as China, France, and Italy without fretting. It also has a worldwide customer base. Diane recently bought a Viennese gaming table in Austria and sold it to a customer in New Zealand for $6,000.

From Global to You is finally whole again. It recently moved into a 42,000-square-foot warehouse and has opened a storefront location in Provo, and the Binghams are building a $750,000 home. Sales in 2003 topped $2.2 million, meaning that the stakes would be even higher if crisis should strike again. But Diane knew about recent virus scares such as SoBig and MyDoom only because she got messages on her computer saying they had been caught before doing any damage. "MyDoom got lots of our clients, but it didn't get us," she says with more than a hint of pride. Another hurdle cleared.