This is something I wish I knew a week ago. While walking with friends on the sidewalk near the Church of the Spilled Blood, an aggressive hawker appeared with a handful of photos offering them for sale. We waved him off and walked quicker. He vigorously persisted, targeting my wife and I. She pushed ahead and we accelerated to the point where we were almost running to get away. He stayed with me for a few steps and then grabbed me around shoulders, momentarily immobilizing me, and said, "My friend! Look at my photos!". I spun out of his grip and he threw his hands in the air and immediately turned away. I took one step and could tell that my camera bag with empty. It had been zipped and buckled with the zippers tucked away and was now totally open and empty, my expensive camera and lens gone. All of this took place in about 5 seconds.
After returning home, a friend put me onto a video he had seen on a popular photography blog last week that was about, you guessed it, a group of organized thieves stealing an expensive telephoto lens right off someones camera in a similar fasion to what happened to me. As a matter of fact, I'm sure one of the men in the video was the lead guy of the group that attacked me. Since then, I've learned of at least two similar attacks which occured last week.
A Russian acquaintance told me that these groups are well-organized and often connected to organized crime and sometimes even powerful local figures which make the police hesitant to do anything.
I've traveled the world, take care in and notice my surroundings and I've been in some dodgy places but I had never seen anything like that. And now, having watched the video of how they operate, I can see that once one is tageted there is really no escape so the only answer is not to be targeted and that means leaving the DSLR at home and taking the point and shoot instead. You may not get to sell the images to Getty but you will be more likely to return home with your gear.