Messengers are dangerous mostly because viruses spread themselves by sending download links to each person on the friends list, people assume it's from a friend so they download it and get infected. The simple solution to this is to never download something from a friend via a messenger, or if you must, be sure to ask the friend if they meant to send the file, and then virus scan it before you open it. I've been using aol and msn messengers for 6 years and have never had a problem. Playing with fire is safe enough when you keep it in the fireplace.