How often are Kidnappings in Mexico City?

I have always been attracted by South America, its people, history, culture etc. I have been to Brazil, Argentina, Chile and I plan on visiting other countries on that continent. But, this year I will go little more to the North, Mexico City. Especially because it is my girlfriends wish. Anyway, some of our friends were there last year and had a great time. Still, there were some tourist kidnappings at the time, which somewhat ruined their holiday. How often are kidnappings in Mexico City?

I know only that several years ago, kidnapping rate was extremely high, second only to Colombia. Further more, not only rich people were victims, even people form mid class were the target of the criminals. There were 160 murders between 1996 and 2004, all connected to abduction cases. There was one recent case that angered Mexican citizens two brothers were killed, with already paid ransom of $600000. Simply terrible. I do not know what is the situation like now, I hope things like these do not happen anymore.