Analysis of the contents of millions of e-mails has revealed that less than 4% is legitimate traffic.Read on at BBC.
Further work has shown that most of this junk mail is originating on hijacked home computers.
E-mail security firm Return Path said 99% of the computers it monitors that send mail have been taken over by spammers or virus writers.
Four percent of e-mail is useful

Mail monitoring firms claim more than 95% of e-mail is junk, be it spam, error messages or viruses.