Imgur images run a hidden .swf file which DOS 4Chan and 8Chan by constantly making get requests
According to another redditor, BackFromShadowban, when an Imgur image is loaded from 4Chan, imgur loads a bunch of images from 4chan’s content delivery network or 8chan (unclear at this point, might be both), which causes a DDoS to those sites.
Apparently 4Chan is now undergoing a DDoS attack due to this Imgur bug. The good news for the image boarders is that Imgur has acknowledged the bug and will be fixing it soon.
@GranPC Hi there, thanks for bringing this to our attention, we're currently working on a solution.
— Imgur (@imgur) September 21, 2015