document: On its Twitter feed, the firm reported a second outage this afternoon - which was restored less than an hour later.
  "Internet of North Korea down again at 15.41 UTC. Second blackout since last night's restoration of service," the tweet read.
  The first outage saw large parts of the internet unavailable in North Korea.
  Officials have not yet commented on the issue.
  Speculation is rife about the source of the blackouts, following a cyber security row with the US.
  China has denounced reports suggesting it was responsible. US officials have not commented on any possible American involvement.
  The US had said it would launch a proportional response to the hacking of Sony Pictures, after an FBI investigation appeared to show that North Korea was behind the hack attack which led to films and private emails being leaked online.
  The Interview, which depicts the assassination of North Korean leader Kim Jong-un, was cancelled by Sony following threats from hackers.
  Internet services in North Korea were down for around nine and a half hours in the first outage, according to Dyn Research.
  Some questioned how much an outage would affect a country where normal citizens have little access to the web.
  Although many have computers and smartphones, they only have access to a government-approved intranet. Access to the world wide web is reserved for a trusted elite in North Korean society.
  North Korea's internet is handled by state-run company Star Join Ventures which is routed through Chinese telecommunications firm China Unicom.
summary: North Korea appears to have suffered a second internet blackout, according to internet performance measuring firm Dyn Research.