SCIENCE AND TECHNOLOGY
The origin of the arroba symbol is not known for sure, but it is believed that it appeared in Antiquity, between the Greek and Roman civilizations to abbreviate the expression of equivalence between the weight of goods.
Over time, the arroba became a unit of measurement, generally used in the animal or grain trade: 1@ = 14.688 kg.
The use of the symbol in computing only took place in 1971, when programmer Ray Tomilson used it for the first time out of pure sympathy and convenience.
Ray needed a symbol that was compatible with most networked systems and that was different enough not to be confused with the characters in people's names. Fashion has caught on and you can't send an email (or tweet) without typing it. He combined the useful with the pleasant by using a symbol that was already known by the nomenclature "at", which in English means the preposition "in". This way, the person's name, added to the @, indicated the location of the email on the network (name@domain.com). Fashion has caught on and you can't send an email (or tweet) without typing it.
Source: UOL Tecnologia – 12 .feb.2011