In the first five months of 2001, leading antivirus vendors detected more viruses than they had in the entire previous year. This development led media outlets such as ZDNet to refer to 2001 as the "Year of the Virus." Not only were more viruses detected, but according to MessageLabs SkyScan virus-scanning service, the ratio of infected e-mail messages to total e-mail messages increased from roughly 1:1,500 to 1:1,000 [4].