There are over 50,000 known viruses. Unlike in the past, today most computers are infected with a virus transmitted via email. On ISPs and company mail servers without real time email virus scanning, one in every 150 emails sent has a virus. Viruses come from many different systems on the internet, mailing lists, list servers, spammers, commercial sites, friends, and business associates. Just about anybody who sends you email can infect your system.
Viruses are of many types.
Some only execute a cute program and do no harm. Others infect your computer, then reproduce themselves and are sent to everybody in your address book. Some can destroy data on your computer as well as send itself. Others will completely destroy your operating system and may even require you to take your computer to a repair shop to be completely restored. To combat this problem and gather more data, NuNet temporarily installed free virus scanning and scanned 7,000,000 emails over 2 months.