Sony's PlayStation Network and Sony Entertainment Network were taken down over the weekend by a distributed denial of service hack and, while back up by Monday, the network is still experiencing glitches. Investigators can't figure out who is responsible.

One hacking group identified themselves as the "Lizard Squad" and claims it also forced authorities to redirect a plane that Sony Online Entertainment's president, John Smedley, was a passenger on by suggesting that there might be a bomb on board via Twitter.

Soon after, another hacker, who goes by the name of "FamedGod," said he was responsible for the hack, and also retaliated against the Lizard Squad for taking credit.

FamedGod is reportedly a member of the hacking group Anonymous and in retaliation he tweeted a list of IP addresses, reportedly those of the members of the Lizard Squad group.

Sony has said that both networks are now back in action, and it is working with the FBI to find the attackers.

DDoS hackers, unlike data breaches, do not steal information but slow the network with repeated requests, so there is little risk to members of either network. Instead, they cause big, expensive problems for the company that owns the networks.

Sony did say that there was no evidence of any intrusion into its network. However, it did not mention which network it was talking about. It also said that there was no evidence of any personal information being stolen.

"DDoS attackers have the ability to be very disruptive to online businesses or businesses that rely on electronic systems to provide services," said Marc Gaffan, co-founder and chief business officer at Incapsula, a Web security company. "Every minute a gaming site is down is a minute of unrealized revenue and an opportunity for a gamer to churn and start playing at a different gaming service." 

Sony has had a number of problems with the PlayStation Network since it was launched. In 2011, a hack exposed personal information for over 100 million users. That breach also happened following a DDoS attack.

According to Verizon there has been an increase in the size of DDoS attacks. In 2011, the average size was 4.7 Gbps. This figure more than doubled last year to 10.1 Gbps. One of the largest DDoS attacks took place in February, totaling around 400 Gbps.

Details about the hack involving the Lizard Squad and FamedGod have yet to be released.

Finding hackers of this kind can be quite difficult to do. Some suggest that social media sites such as Twitter would be safer if users had to sign on with their real identities. However, many social media sites suggest that online anonymity is more important.