More than 97% of all e-mails sent over the net are unwanted, according to a Microsoft security report.
The e-mails are dominated by spam adverts for drugs, and general product pitches and often have malicious attachments.
The report found that the global ratio of infected machines was 8.6 for every 1,000 uninfected machines.
It also found that Office document attachments and PDF files were increasingly being targeted by hackers.
Microsoft said people should not panic about the high levels of unwanted e-mail.
Cliff Evans, head of security and privacy for Microsoft in the UK, told BBC News: "The good news is that the majority of that never hits your inbox although some will get through."
ITU Global Cybersecurity Agenda