One of the most useful features of home PCs is that, unlike the people that use them, they don't forget anything.

When your PC is connected to the internet, information about the web pages you have visited and emails you have sent or received are all saved somewhere.

While this brings many benefits, the rising tide of pornography that threatens to flood the internet has caused much worry among Computeractive readers, prompting many of you to ask us whether you face any legal liability for images that find their way onto your computer.

To help clarify the issue, we will tell you just what your responsibilities are. We'll also show you how to protect your family by preventing inappropriate material finding its way into your home in the first place and how to cleanse your PC of internet filth.

Much of the inappropriate material that finds its way onto your computer does so without your knowledge, via pop-up windows or spam from adult websites.

It is not uncommon for family members to see questionable images or websites, whether intentionally or by accident, without your consent.

Recent police investigations involving paedophile rings and unfounded allegations against well-known celebrities have heightened public sensitivity to the issue of internet pornography.

Many people now worry that images stored on their PCs by pop-ups or via inappropriate use by others could get them into trouble, particularly if the computer has to be examined by engineers for repair.

Laying down the law
Detective Inspector Terry Jones is in charge of the Abusive Images Unit at Greater Manchester Police. His team was set up in 1978 to combat the distribution of indecent images of children and has been focusing on the internet and newsgroups since 1995.

He stated that there is only one form of indecent material that you could face legal consequences for possessing. "A person in the UK can lawfully possess any form of sexually explicit material on their computer other than indecent images of children under 16," he said.

Even material that most people would find bizarre and distasteful is legal. "Most pornography involves consensual activity among adults," explained DI Jones.

"The material we target is mainly young children and toddlers facing abuse. It's a world apart from most of the material that you see on the internet as far as the law is concerned."

A disturbingly high proportion of the pop-ups and spam that you may encounter offer access to precisely this kind of material and even show you a sample of their wares. Don't worry: you will not face legal problems simply for being a passive recipient.

"We make a common sense judgement about the context of material," explained DI Jones. "A PC provides a detailed record of what it has been used for that is very difficult to tamper with.

"If we make a decision to prosecute, we have to prove that there was an intention to collect the material so we look at the whole process by which it ended up on the computer.

"We're not after people who, through no fault of their own, suddenly find a link popping up on their screen. We're looking for people who methodically search for this material."

A ruling made in 2002 in a court case against two men reaffirms the point made by DI Jones about intent.

The court ruled that "the recipient of an email attachment containing an indecent image of a child would not commit an offence by opening that attachment if they were unaware that it contained or was likely to contain an indecent image".

So the best course of action to take when an indecent image is forced onto your computer is to delete it. Under no circumstances should you respond by clicking on it or by replying to spam.

A desire to complain to the sender or to investigate whether whatever offered is illegal with a view to reporting it to the authorities is often understandable, but it could land you in hot water.

Accessing any website that offers paedophile content or sexually suggestive images of children could be interpreted as an active search for illegal material. Besides, if you reply then you give your email address to the perpetrators and you will probably get more spam as a result.

If other people use your computer, you may fear that you could be held responsible for material that they have accessed.

But DI Jones said that the police would be unlikely to prosecute simply because you were the owner of a PC found to contain indecent images of children.

"We adhere to the same investigative standards as we would on a drugs seizure," he explained. "We have to make sure the person we prosecute is the right one. That's where the PC itself helps us, as we can compare the times illegal material was viewed or downloaded with a suspect's movements."

Some technically savvy people may be able to mask their activity but most viewers of pornographic material online are unlikely to have such skills.

Distribution of indecent images
While possessing pornographic images other than those involving children on your PC is legal, distributing them to others using email or by publishing them on a website is not allowed under the Obscene Publications Act.

This vague piece of legislation states that it is illegal to distribute material that will "corrupt or deprave" the recipient.

While you are very unlikely to be arrested for doing so, the best advice is to use your common sense and never forward an email or image that could be considered indecent or publish it on your website.

Family photographs
But what about innocent photographs of your own family? It is not unheard of for photographic developers to tell the police about images of young children that they have deemed to be indecent.

DI Jones explained that decency is a matter of context. "With digital photography becoming more popular, we have had PC repair engineers report images to us that they have thought might be inappropriate," he said.

"We simply make a common sense judgement. Parents take pictures of their children all the time and inevitably some of those images will contain nudity."

Although it is an offence to possess an indecent image of a child, the nature of indecency is not defined in law. DI Jones said that normal family photographs are very unlikely to attract such attention.

"It's difficult to explain the difference between a picture that shows a loving family scene and one that shows an act of abuse without actually seeing the two compared," he said.

"But when police officers look at images, the difference between what is appropriate and what is not is obvious."

DI Jones added that you should not allow the illegal activities of criminals to affect the way you use your computer or the internet.

"We shouldn't begin to change our way of life because of sexual abuse of children by criminals. It acts as a cancer on our sense of what is proportionate. I understand people's worries but you have to keep things in perspective," he said.

Preventative measures
The good news is that much of the material that may offend you can be prevented from reaching your computer in the first place, and there are tools you can use on a regular basis to keep your PC free of smutty material.

Just because your PC is unlikely to lose any images that have been downloaded, you can check for inappropriate material by using the Windows search facility (see below).

Web filtering software can be used to block material from pornographic sites, and pop-up ad stoppers block most irritating advertisements.

You can also prevent other users of your PC from accessing pornography by setting filters in your browser.

Parents should also take an active interest in the use children make of their time online to ensure that curiosity does not expose them to unsuitable material.

Reporting indecent images
Although much of the material you see on pop-up and spam emails is distasteful, it is not actually illegal in this country so there is no point in reporting it to the police.

Indecent images of children are a different matter. Sites offering such material should be reported to the Internet Watch Foundation, the body that co-ordinates the fight against child abuse images on the web. Visit its website at www.iwf.org.uk for more information.

Bear in mind that the senders of such material are usually based overseas so it is difficult for UK authorities to pursue or close them down.

The naked truth
We hope that you now feel reassured that the only people who should fear legal repercussions from internet pornography are those involved in the production and distribution of images of child abuse or those methodically amassing collections of such material.

As DI Jones says, it would be a shame to allow a few criminals to spoil your enjoyment of the internet and digital photography.

"There is no benefit to the police in pursuing innocent people. Web filtering software and the tools that people need to stay safe on the web are out there," he said.

"Computers and the internet have actually made our job much easier because they provide hard evidence of child abuse and an electronic trail back to the abusers."

KEEPING IT CLEAN

Some of the basic housekeeping tips that we always recommend to keep your PC in shape will clear out images that have turned up on your PC.

Deleting temporary internet files and clearing your History folder in Internet Explorer will flush out unwanted images from sites that you have visited.

Bear in mind that moving images to the Recycle Bin on your Desktop and then emptying it does not delete the image from your hard disk straightaway but makes the disk space available for overwriting.

SEE WHAT IMAGES ARE ON YOUR PC

In Windows XP:
Select Search from the Start menu and click on Pictures, Music and Video. Click on Use Advanced Search Options and tick the box marked Pictures and Photos before clicking on More Advanced Options.

Click on the drop-down menu with Look In written above it and choose Local Hard Drives. Make sure the following boxes are ticked: Search System Folders, Search Hidden Files and Folders, and Search Sub-folders.

Finally, click on the Search button. The search may take a few minutes depending on the speed of your computer and the size of your hard disk but it will reveal every picture stored on your computer.

To simplify viewing the stored material, click on the Views button and select Thumbnails to see the images.

In Windows 98:
Select Find from the Start menu and click on Files and Folders. Type *.jpg; *.gif into the empty box titled Named.

From the drop-down menu marked Look In, select My Computer and make sure the box marked Include Sub-folders has a tick in it.

Finally, click on Find Now. The search may take a few minutes depending on the speed of your computer but it will reveal every JPEG and GIF picture file stored on your hard disk and other storage devices connected to it.

Unlike Windows XP, Windows 98 will not let you view the results of the search as thumbnails but if you select Details from the View drop-down menu at the top of the screen, you will be able to examine the names of image files on your PC to help you spot anything untoward.

PROTECTING YOUR PC

Computeractive has arranged a free, three-month trial of CyberPatrol for all readers. Go to www.cyberpatrol.com/offer and type Computeractive as the promotion code.

This web filter won our Buy It! award in the filtering software group test. If you want to buy it after your trial, the price is £34 for a 12-month subscription.

McAfee Parental Controls from www.mcafee.co.uk is simple to use and offers effective protection for your family for £20 (see issue 131)

NetNanny 5, available at www.netnanny.com, also offers great protection and represents good value at £34.

Pop-up Stopper is available free of charge from here.

AdAware is available free of charge from here