Deadly virus epidemics that could kill everyone

There have been a lot of hollywood movies and tv shows about virus outbreaks like Contagion or The Walking Dead but could something like that really happen? Could there be a super virus that has a high mortality rate and can kill very fast but not too fast so that the virus has time to reproduce and spread to other people? 
 Rabies.
 Rabies is the most deadly virus when it comes to case fatality rate (which is 99% if left untreated!). I know there has not been made a very exciting movie about rabies (like about an Ebola like virus, in "Outbreak" with Dustin Hoffman), but it does need full attention. The case fatality rate of Ebola is 50-90%, and not 99%, like in rabies. It's an awful disease, which can be prevented by vaccination and post-exposure treatment. The symptoms are horrible: confusion, agitation, anxiety, abnormal behaviour, partial paralysis, insomnia, paranoia, terror, hallucinations, progressing to delirium. As patients suffer from paralysis in their throat, they have difficulties drinking, so they refuse to drink. This is called hydrophobia. The primary cause of death is usually respiratory insufficiency. During my medical training, one of my teachers showed us videotapes of patients with rabies. After having seen this, I don't agree with the statement that Ebola is the disease in which the infected suffer the most. I'm glad I had my rabies vaccinations! 
When it comes to numbers of patients who die of a viral disease, we could make the following distinction: 
- Most deadly virus all time: Influenza (probably > 100 millions deaths) 
- Most deadly virus nowadays: HIV (2 million deaths each year) 

Influenza. 
The 1918 spanish flu infected 500 million people and killed 50-100 million in 9 months, from march till November 1918, making it the deadliest virus in history. Also, when one third of the world's population is sick or dying, all hells breaks loose. The dead cannot be buried and the sick can not be taken care of. The killer virus is knows as Influenza A virus subtype H1N1. Do not mess with the flu! 
Overall the Influenza virii are very dangerous, because they mutate all the time and are easily transmittable (airborne). 
Influenza also beats the black death (caused by the bacterium Yersinia pestis) in terms of killing speed. The plague killed about 75 million in many years. 
HIV doesn't even come close (estimated at 25 million kills since 1981). 


If someone was able to genetically modify a virus to have a mortality rate as Rabies, kill very fast but not too fast so that it has time to spread to different people, and could survive in most climates and release the virus into a high populated area like an airport where it could be transferred across different continents and countries then it is very likely that a virus like this could kill a large percentage of the population. A small percentage are bound to survive in an event like this due to natural immunity to the virus. If the virus was to mutate, it could kill the remaining population and actually cause the human race to go extinct.
It is a very likely possibility that something similar to this could happen. Make sure you wash your hands frequently and don't shake peoples hands because the virus outbreak can arise at any time!