An organization advocating for lower bus fares initiated the protesting last week, but demonstrations have since ballooned with no centralized leadership. Groups of Brazilians also staged small protests Tuesday in other countries, including Portugal, Spain and Denmark.A cyber-attack knocked the government's official World Cup site offline, and the Twitter feed for Brazil's Anonymous hackers group posted links to a host of other government websites whose content had been replaced by a screen calling on citizens to come out to the streets. Tuesday's march in Sao Paulo started out peacefully but turned nasty outside City Hall when a small group lashed out at police and tried to invade the building. Different groups of protesters faced off, one chanting "peace, peace" while trying to form a human cordon to protect the building, the other trying to clamber up metal poles to get inside. At one point, one person tried to seize a metal barrier from another who was trying to use it to smash the building's windows and doors. The air was thick with police pepper spray and smoke after demonstrators set a TV satellite truck and a police lookout booth on fire. Vandalism and violent clashes with police similarly marred the end of Monday's mostly peaceful march in Rio, which left the city's downtown stinking of tear gas. That march attracted some 100,000 people, ending with a small splinter group doing an estimated $1 million in damage to the historic state legislature building. Another mass protest is planned for Rio on Thursday. The protests have raised questions about the country's readiness to host the coming high-profile events including a papal visit to Rio and rural Sao Paulo next month. Brazil is playing host this week to the Confederations Cup, which is seen as a warm-up for next year's World Cup. Police and military had spent the past year pacifying hillside slums in Rio to prepare for the events, even as the grievances were apparently growing among the country's middle class.