The black art of spamming has grown ever more Machiavellian since the start of the year, according to new research.

Secure messaging firm FrontBridge claimed that the use of deceptive subject lines in spam has grown by half this year.

Gone are the days of obvious spam, when a cursory glance at the subject line of a mail encouraging you to 'Buy Viagra online' or 'Enlarge your breasts' was all that was needed to prompt you to hit delete.

Now, recipients are more likely to be invited to answer a question, rather than begin a quest for answers to inadequate body parts.

FrontBridge highlighted the top 10 most common subject lines used to try and con victims into opening spam.

Top of the pops is 'RE: Information you asked for', which implies that the user has requested something.

Second up is 'Hey', which is the most common friendly intro used in email. At three is 'Check this out!' which is the most common intro to a friendly forward.

Following at four and five are 'Is this your email?', in which the spammer poses as an old friend, and 'Please resend the email', which implies that you are already in communication.

Six, seven and eight aim to play on recipients' fears with 'RE: your order', 'Past due account', and 'Please verify your information', which again implies previous communication.

Nine is 'Version update', which most probably implies a fake software update via email.

And rounding off the top 10 is 'RE: 4th of July', which guesses at holiday plans for the Fourth of July public holiday in the US.

But spammers now continually vary the subject matter, and many take the approach of worrying the recipient into opening the message, such as 'RE: late payment'.

Merely opening such emails can, unfortunately, unlock a Pandora's Box for users of the preview pane in programs such as Outlook, inviting Trojans, viruses, browser launches and pop-up ads.