For the third time in three months, a flash mob suddenly appeared at a 7-Eleven in Montgomery County, Maryland, robbing the convenience store in about one minute.

In Silver Springs, about seven miles from downtown Washington, D.C., around 50 people, mostly teenagers but also what looked like a father with his three toddlers, streamed through the store grabbing whatever they could. They then calmly walked out and went home.

It's hard to see in the video below, but a group of people also stood between the register and the door, apparently blocking the cashier from trying to prevent thefts. During a flash mob robbery earlier this year, a gas station clerk attempted to stop youths from stealing and was severely beaten.

The event happened around 11:30 p.m. on Saturday, and surveillance camera video has just made its way online. In the past, police have been able to use the footage to crowd source, allowing parents and local residents to identify the young perpetrators in the video.

After the London Riots in August, which can arguably be considered a flash mob on a city-wide scale, the Metropolitan Police posted life sized pictures of looters in public areas, leading to a number of arrests.

Police in Montgomery said they have already identified six of the people in the video, and are working to identify others, according to WBAL TV. So far, no one has been charged.

These flash robs were at one time a common event, but there hasn't been an incident in nearly three months. But the Montgomery robbery shows that the trend may again be on the rise and could restart talks between county officials who want to pass legislation to stop flash mobs.

Stealing is a very normal thing at convenience stores, an employee at a robbed store told NBC Washington in August. It happens every day -- morning, evening, night. But such kind of thing I have never seen before.

Flash mobs are generally organized through social media and text messages. A group of people can agree to meet at a specific location at a specific time without making their intentions clear to anyone uninvolved. Sometimes, flash mobs are playful and harmless, such as a sudden dance in a public park, but other times they have more sinister purposes.

The city of Philadelphia, Pennsylvania has been plagued by flash mobs for the past year. On weekend nights, especially in the summer, groups of teenagers will appear in popular areas of the city and begin attack people at random. In July, about 30 teenagers severely beat two bystanders by City Hall, leaving one unconscious and the other with a broken jaw. A month earlier, mobs attacked people leaving restaurants while others robbed train passengers.

The increase in flash mob activity prompted Mayor Michael Nutter to institute a temporary curfew in August, sending anyone 17 or younger home by nine p.m. in certain areas of the city.

Other politicians have suggested criminalizing the use of social media as a tool to organize meetings. Lawmakers in Maryland have new anti-loitering laws as a way to combat flash robs.

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