Email is known to be one of the most popular infection vectors. Figure below shows countries ranked according to the quantity of malicious files sent from servers located in a specific geographical location. The USA, Germany, Sweden, Spain and Malaysia are the top five countries to send infected emails. Email worms make up more than half of all malware spread via email (55%) This type of malicious program is not only circulated via mass mailings by cyber criminals but is also capable of self-propagation. Virus writers used the updated version of Zhelatin to develop a network of zombie computers (botnets)”]
Source: https://securelist.com/kaspersky-security-bulletin-2007-malware-which-spreads-via-email/36191/