I thought I posted about this a while ago, but if I did I can't find the post.
More than 100 varieties of Mexican candy have tested positive for extremely high lead contamination and are unsafe to eat. The OC Register has a special investigation section about these "Toxic Treats" with a lot more information. It's most recent article in the investigation is from April 30th, 2005, and says that despite years of warnings the lead contamination is still a huge problem.
The FDA also issued a warning about lead contamination in Mexican candy last year, and the Department of Health issued an extended warning in 2001. This is an ongoing problem that people should be aware of, especially anyone who might regularly eat Mexican candy.
Wikipedia has more on lead poisoning, and points out that it affects children most significantly and that many studies have shown links between lead poisoning, learning disabilities, and violent tendencies.