Critics have long warned against the inherent dangerous nature of DNS blocking, and how innocent websites can be caught, and a recent incident in Denmark is again proving the critics right.
On Thursday, the Danish Police accidentally blocked 8,000 legitimate websites due to a mix up of two lists, one containing banned websites, and another "whitelist" containing a list of legitimate websites. At a flick of a switch, websites such as Google and Facebook were blocked for users of the ISP Siminn, and it took more than 3 hours for the problem to be spotted and cleared up.
The agency responsible for handling the blacklist, The National High Tech Crime Center of the Danish National Police (NITEC), blamed the mistake on "human error". NITEC maintains a blacklist that blocks websites featuring indecent images of children amongst other illegal materials, a list that ISPs can voluntarily download and implement. The mistake occurred when an employee accidentally uploaded the wrong list, as present operating procedure at NITEC only requires one employee to be responsible for uploading the entire nation's blacklist. Luckily, only two ISPs were affected as not all ISPs had "downloaded" the central blacklist before the mistake was ultimately corrected.
Technology activist IT-Political called on ISPs to drop their support for the voluntary program. "Today’s story shows that the police are not able to secure against manual errors that could escalate into something that actually works as a ‘kill switch’ for the Internet," the group said in a statement.