By Denise Winterman
BBC News Magazine
It has led to the downfall of many. Now the government is arranging the deletion of millions of e-mails. But is it really as easy as hitting a button on the keyboard?
E-mail has a long memory, as former home secretary David Blunkett can confirm. Forced to quit last week after e-mails containing damaging information were discovered, he is the latest in the long line of people to be haunted by cyber mail.
It has now emerged that civil servants are being told to destroy millions of e-mails. The government says it is in the cause of good information management, but some people have pointed out that in a fortnight's time, they will become publicly accessible under freedom of information legislation. However, as many have discovered, it is not as easy as hitting the delete key.
What may look a simple task is extremely complex in reality. Even if you regularly clear out old e-mails from the inbox and the "deleted items" folder, several copies of any message are likely to have been sent into cyberspace.
"There is always a trail to find," says Tony Dearsley, senior computer investigations manager with computer forensics firm Vogon.
"When you hit delete and empty your 'deleted items' folder it just gets rid of e-mails from public view. A lot depends on the system you use, but to guarantee something is permanently deleted is very difficult.
"Fragments of data are left lying on the surface of the hard drive, showing where you've been."
When a message is deleted, it does not immediately disappear. The computer writes a tag that instructs the message to be overwritten if that chunk of memory is needed. But with the huge capacity of modern hard disks, this is a rare event.
The fact that mail tends to pass through several different servers before it reaches its destination also means there could be several different copies of it in existence. Most company servers, for instance, will retain a copy of sent and received e-mails for months.
"In some aspect an e-mail can exist indefinitely," says Mr Dearsley. "Subject lines, times and dates can all be pieced together. I have retrieved some that have been years old."
Often people are unaware when an e-mail is copied. Most firms now filter e-mail to stop viruses and spam and any unsuitable content, in the process records of those e-mails are logged.
A lot of companies are still not very good at doing this. A survey carried out by software company KVS found only 19% of the firms questioned had any reliable way of recovering e-mail more than a year old.
But cyber sleuths can be called in to retrieve all sorts of information that a user believes has long gone.
And by piecing the information together experts can get a good idea of the type of person they are dealing with, what their interests are and what their level of technical knowledge is, says Mr Dearsley.
So it may say delete on the key, but in cyberspace getting rid of information is easier said than done.