Romania was home to the infamous vampire Count Dracula so perhaps it shouldn't be such a surprise to learn that it is home to many of the Zombies associated with the Storm BotNet. The term "Zombie" is commonly used to describe a home PC that has been compromised and is under the central control of a master to send spam. Storm has evolved so that it no longer has an army of zombies under one central control, rather it behaves like an army of vampires, divided into small groups where each machine has the ability to assume control should one be killed.
Typically when Anti-Spam companies publish metrics related to spam or infections per country allowances aren't made for the size or population of the country so it shouldn't be a surprise that the USA is seen time and time again. However, by looking at the number of machines recently infected by the storm worm in each country and normalizing by the number of Internet Users in that country, we see the following ranking: