When something goes wrong on the Internet, monitoring firm Renesys is watching. Since 2000 the firm has tried to be the first to notify customers when Internet transmission goes dark, whether it's because of political strife or an undersea cable malfunction. Earlier this week, the company noticed another service outage in Syria's embattled Aleppo region.

On Thursday, New Hampshire-based Renesys announced that it was being acquired by Dyn, which monitors and manages its customers' Internet traffic. The sale price was not disclosed. Both companies are privately held.

The acquisition reflects Web companies growing concern about the instability of the Internet. Internet outages have become more noticeable: Entire countries sometimes go off the map — or traffic gets mysteriously rerouted.

"The world has become very flat when it comes to Internet usage," says Jim Cowie, Renesys' head of research and development. And that means more demand for intelligence about the status of the global Web, which can be volatile, he said.

Also based in New Hampshire, Dyn grew out of  a project at the Worcester Polytechnic Institute. Founded in 2001, it initially focused on dynamic domain name service technologies. In 2008, it shifted gears — selling a premium service primarily aimed at performance assurance for Web traffic and messaging.

Business has been booming, said Dyn's Chief Revenue Officer Kyle York."We've had 21 straight quarters of revenue growth, quarter over quarter," he says, adding that revenue grew 61 percent in 2013 and 59 percent in 2012. Dyn claims about 850,000 individual and small business customers as well as 3,500 enterprise clients like Twitter, Pandora and Netflix. 

"Of the Alexa 1000, we work with 105 of them today," York says, referring to traffic rankings compiled by Amazon.com-owned traffic-analysis firm Alexa. (Disclosure: The Washington Post is owned by Amazon chief executive Jeffrey P. Bezos.)

Dyn now employs more than 300 people -- 200  of them at its New Hampshire headquarters, with additional offices in San Francisco, Britain and Australia. It expects to open up offices in Latin America by the end of the year. That global expansion is one of the reasons the Renesys acquisition made sense to the company.

"The global view that these guys have when it comes to online availability and threats is second to none," York says, and that could help Dyn expand its real-time capabilities. The company plans to integrate Renesys' global-monitoring data into the services, giving customers insight into where there could be potential problems and finding the most effective ways to re-route.