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. When a user clicks an Imgur image which is a screen cap from 4Chan or 8Chan, the underlying Javascript will first open up two iframes which are moved 900 pixels off the monitor screen and are invisible to the user.  It will then send request to load another ~500 images from 4Chan/8Chan and cause overwhelming data requests to crash the 4Chan and 8Chan websites. 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.

— Imgur (@imgur) September 21, 2015