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 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.