It was about three years ago. One of the company's 120 pet hospital offices got hit with a Web-born virus. Already concerned that employees may be spending too much time on social networking sites, management decided that it was time to rein in Web surfing with some strict controls over where users could go on the Internet. "From that point, we just threw in the towel and said no more," said Aaron Brown, a technology project specialist with the company.

Brown's story isn't unique. The Web has become a dangerous place of late. According to security vendor Webroot, Web attacks are up 500 percent over the past two years, and 85 percent of malicious software is now distributed via the Web.

That's made Web blocking more important to business customers, but sometimes products that do this are too expensive or complex.

Three-year-old OpenDNS is best known as a free ad-based filtering service that is popular with schools, small businesses and home users. But last year, the company hired a new CEO, VMware's former security chief Nand Mulchandani. Under his leadership, it has begun selling its services to larger companies like National Veterinary Associates, a company in Westlake Village, California, that employs about 2,200 people.

On Monday, the company started talking about a new product, OpenDNS Enterprise, which it says it will ship by year's end to be sold on either a per-user or per-site basis. OpenDNS is also working on an ad-free consumer service that will cost less than US$20 per year.

Like the free service it's based on, OpenDNS Enterprise does not have all of the features that enterprise users can get from a larger company such as Websense. But because it uses the DNS (Domain Name System) system to do the filtering, it's extremely lightweight -- administrators turn it on by making some basic settings changes in the PC or router -- and it's less expensive than many products out there.

That's made it a good choice for administrators who have to remotely manage systems in a lot of locations.

It may also give it some traction with small- and medium-sized businesses, which have not been particularly well-served by many Web filtering vendors, according to Paul Roberts, an analyst with the 451 Group. As they look to renew licensees this year, "secure Web gateway vendors, whether it's Websense or Blue Coat, are encountering push-back," Roberts said. "Part of it is the economy and part of it is that there are other options."