Illinois gets more spam than any other US state, according to a study by web security firm MessageLabs.

The study analysed spam traffic on a state-by-state basis and found that 92.1 per cent of all email to addresses in Illinois was spam. The least spammed state was Montana at 77 per cent.

"The varying spam levels can be attributed to different socioeconomic factors and levels of security awareness in each state," said Matt Sergeant, senior anti-spam technologist at MessageLabs.

"The states that are experiencing higher spam levels may not place as high a priority on IT security, or employees and businesses may be more willing to share their personal contact information in public domains.

"When email addresses are openly available, spammers take advantage of it and inundate those inboxes with massive amounts of spam."

Overall, the US is still receiving more than its fair share of spam. Global spam rates are 81.5 per cent, whereas for the US as a whole the rate is 86 per cent.

Sergeant said that spammers were becoming more devious in their efforts to get around filters aimed at blocking content.

Spammers are turning to managed services like Google Docs to ensure that people read their messages, and sending out more targeted emails to smaller groups.