It's fast and easy, but no e-mail is totally secret as Claire Swire discovered when she sent a sexually explicit message to one of her friends.

Within days it had been read by millions of people across the world.

The world of electronic messaging throws up a range of security issues and users should watch what they write.

Every time an e-mail message is sent, someone somewhere will probably be able to read it if they really wanted to.

To get to its destination the message travels via several computers where it could be opened.

Ray Hatley, editor of our evolution pages, said: "E-mail is the most insecure form of communication there is.

"The best course of action is to not send anything in an e-mail which you don't want the entire world to read."

26-year old Claire Swires learned the hard way about the problems of keeping an e-mail secret.

Yesterday she was staying with her parents near Uckfield after a saucy message she sent to her friend Bradley Chait hit the national headlines.

Mr Chait, 27, who works for a top City law firm, is now facing disciplinary action after he forwarded her message to friends at work.

Within a week it is estimated millions had read it and the e-mail had been sent as far away as Australia.

The situation proves the power and speed of the internet in spreading information all over the world.

John Helmer, marketing manager of Hove-based firm Academy Internet, agreed the immediacy of e-mail can lead to problems.

He said: "It is instant and as such can often lead to a rash form of communication.

"People often don't think about what they are writing or doing and send the message immediately.

"Once they've pressed the button there is no going back."

Mr Helmer, whose employers are one of the largest internet training companies in Europe, said e-mail users often did not appreciate the tone of their message and consider how they could be interpreted.

He said: "Everyone is used to controlling the tone of their voice on the phone but it is incredibly difficult in an e-mail.

"Arguments can soon escalate because people take a message the wrong way."

Miss Swire's embarrassing episode was caused by an indiscretion by one of her friends and there is little she could have done after Mr Chait forwarded her message.

But even if he had decided to keep their correspondence secret, the contents of their electronic conversation could possibly still have been read.

Recent laws allow employers to access e-mail accounts of their staff at work and hackers, if they are smart enough, can snoop through any electronic messages not amply protected.

The Regulation of Investigatory Powers (RIP) Act passed earlier this year means public and private sector employers can monitor or record communications without consent in a wide range of situations.

Technology exists for managers to receive a copy of all incoming and sent e-mails from every computer in their business.

Patricia Hewitt, the Government's e-commerce and small business minister, has denied the rules will create a 'big brother' situation in the workplace.

A spokesman for the Department of Trade and Industry said: "Everyone has assumed it would form a spy culture in companies which is not the case.

"Previously it was illegal for companies to access their employees' e-mails which caused a problem in cases like when staff were off sick and information was needed."

But the new law has been criticised by trade unions. The TUC believes it contravenes human rights because it infringes on people's right to privacy in the workplace.

To escape what most lawyers accept is a 'grey area', some firms have imposed policies prohibiting all personal use of e-mail.

In more extreme cases, staff have actually been dismissed for abusing their employer's e-mail system.

Outside the workplace, not even personal messages sent on home computers are safe from prying eyes.

Clever hackers can access most personal e-mails if they try hard enough.

But messages locked with a code are harder to crack. These encryption codes work by using a series of electronic public and private keys held in the computers of senders and receivers of e-mails.

The more complicated the code, the harder it is to solve.

Argus columnist Andrew Hardy, who runs Worthing-based DoubleClick-it, said: "It is possible to send a message which is almost totally secure.

"But to be safe people should regard every e-mail as something which could be read by a stranger.

"Hackers break into e-mail accounts to prove they have the skills to do it."