Social networking websites such as Facebook and Twitter helps users mobilize around a common cause. But what if their message is one of hate? The Simon Wiesenthal Center, a group working against global racism, has compiled a list of hundreds of websites it deems hateful and is pushing their host sites to remove them.

At the White House, President Barack Obama welcomed Myanmar President Thein Sein, the first Burmese leader to visit Washington in nearly five decades. Ray Suarez talks to Jennifer Quigley of the U.S. Campaign for Burma and Priscilla Clap, former chief of the U.S. mission in Myanmar, about reforms in that country.

In Syria, Assad government troops pushed to retake a strategic town close to the Lebanese border. Hezbollah fighters joined the Syrian regime army in laying siege to Qusayr, home to 40,000 civilians. Judy Woodruff reports on the growing involvement of Hezbollah in the Syrian conflict.

In other news Monday, a wave of sectarian killings across Iraq left at least 95 people dead. It was the single-worst day of violence in Iraq in more than a year and a half. Also The New York Times reports that computer hackers in the Chinese military have resumed attacks on U.S. companies and government agencies.

The rescue effort after the Oklahoma twister that killed 24 people nears an end, as it emerges the storm was more powerful than thought.

Iran's President Ahmadinejad says he will contest the disqualification of his ally Esfandiar Rahim Mashaei from next month's presidential poll.

German software company SAP says it hopes to recruit hundreds of people with autism, saying they have a unique talent for information technology.

EU leaders will seek to curb tax evasion, which costs EU states 1tn euros a year, and bring down energy prices to boost competition.

By 2017, the Alaskan town of Newtok could be completely underwater, leaving 350 residents adrift.

With the death of a possible suspect, activists are weighing the FBI's efforts to tackle the cases.

The Ruth Ellis Center is making an effort to meet its clients where they are — on the dance floor.

One of the victims in a triple murder may have been a friend of bombing suspect Tamerlan Tsarnaev.