The user will not even be warned this is happening - the only message that appears is 'loading'.

 

The email automatically downloads malicious software into your computer from elsewhere the moment a user clicks to open it.

 

The mails themselves are not infected - and thus will not 'set off' many web-security defence packages.

 

Security experts say that the development is 'particularly dangerous'.

 

'This sort of spam also affects cautious users which would never open an unknown attachment or link,' say security experts Eleven Research Team.

 

Previous generations of email-borne viruses and trojans required users to click on an attachment - often an office document such as a PDF.

 

The new emails - dubbed 'drive-by emails' - have been detected 'in the wild' by computer researchers Eleven Research Team.

 

'This driveby spam automatically downloads malware when the e-mail is opened in the e-mail client,' says Eleven Research Team.

 

'Previous malware e-mails required the user to click on a link or open an attachment for the PC to be infected.'

 

The new generation of e-mail-borne malware consists of HTML e-mails which automatically downloads malware when the e-mail is opened.'

 

'This is similar to so-called driveby downloads which infect a PC by opening an infected website in the browser.'

 

The current wave of emails arrive with the title 'Banking Security Update.'

 

To stay safe, the security company advises switching all security settings in email software to maximum, and updating your browser to the latest version so it's protected against malicious software.