CAIRO – Amid heavy security Monday, Egypt marked the fifth anniversary of the uprising that toppled longtime autocrat Hosni Mubarak, with activists taking to social media — but not the streets — to express frustration that their demands for freedom and democracy had not been realized. Since 2011, when Mubarak fell after nearly three decades in power, Egypt has seen much upheaval: the rise of President Mohammed Morsi and his once-banned Muslim Brotherhood; the ouster of Morsi by Abdel-Fattah el-Sissi, a former general; and El-Sissi's launch of one of the harshest crackdowns in years, with the jailing of thousands of Islamists and scores of liberal, prodemocracy activists. An icon of the uprising, Wael Ghoneim, urged others not to be discouraged. "The January Revolution will only be defeated when everyone falls silent," he said, addressing activists. "Don't despair. Don't be silent. Your words are a revolution."