The Zara T-shirt called the “Sheriff” went on sale online at 2 a.m., London time, on Wednesday.  Within a few hours, it had sparked a social media outcry, with many Twitter posts accusing the clothing company of anti-Semitism — or at least a large measure of insensitivity. The shirt, meant for children, bore a striking resemblance to the top of a Nazi concentration camp uniform.

Why? Because it’s becoming pretty obvious that Isis’s most effective weapon is the smartphone. The group has been using Twitter, Facebook and YouTube to great effect, to create a digital broth that has both panicked and fascinated us. Their graphic videos make front page news and their deranged tweets sway international diplomacy. Social media strategists round the world must be watching in awe.

With terrorists running rampant in Iraq and Russian convoys violating Ukrainian borders, the U.S. State Department is fussing over a new unnerving threat: its own diplomats taking the “Ice Bucket challenge.”  The ice bucket challenge is this summer’s social media fad with a philanthropic twist (donations go to the ALS Foundation, which funds research to fight Lou Gehrig’s disease).

The ruling party has told all 86.6 million of its members to engage with its first foray into social media with a public account launched this month on massively popular mobile social media platform WeChat, which boasts 438 million monthly active users. The account, called “gong chan dang yuan”, or Communist Party member, is managed by the Organisation Department of the party’s highest organ of power, the Central Committee. The department has told all members of the world’s largest political party to follow the account.

Capitalizing on the immense popularity of the ALS ice bucket challenge, an Indian woman has conceived of the rice bucket challenge as a way to encourage charity for the poor. Unlike the ice bucket challenge, which requires the participant to dump a bucket of cold water over their head, the rice bucket challenge asks that participants simply donate a bucket of rice to somebody in need.

At first glance, it seems obvious -- of course Twitter and YouTube have the right to take down a video showing the American journalist, James Foley, being beheaded. The question is why taking it down is controversial at all. The answer, I think, shows how important services like Twitter have become, and how this has thrust unexpected responsibilities onto them.

For about three hours Wednesday morning, the Ukrainian flag was flying high over Russia’s capital city. Protesters fastened a blue-and-yellow banner to the Soviet star atop the spire of one of Moscow’s Stalin-era “Seven Sisters” skyscrapers on the Kotelnicheskaya Embankment about a mile from the Kremlin.