A web designer in London was amazed to discover that Iranian election protesters are attacking the Iranian president’s Web site using software he developed in his spare time, he told CNN Wednesday. With anti-government activists in Iran sidestepping official attempts to silence them on the Internet by posting photos, videos and blogs on sites like Facebook and Twitter, others are using a site that automatically refreshes a Web page every few seconds, potentially overloading the host server. The page reboot software means that dissidents can “attack” sites with a barrage of hits — known as a denial of service attack — causing them to appear to users as “unobtainable.” Iranian President Mahmoud Ahmadinejad’s Web sites was one of those displaying this message on Monday, according to Britain’s Channel 4 News, although on Tuesday it was loading correctly.