Safe Computing on the Internet

Notes on computer security for the home user

There is no reason why you should ever have a computer virus infection, or have to reinstall your computer because it doesn't work properly. You should also be perfectly safe to pay for things over the Internet with your credit card, and use your computer for on-line banking. Read these notes to find out how...


You should never connect a computer directly to the Internet. You should connect it via another device that acts as a safety filter: it allows your computer to connect to the Internet, but the Internet isn't able to connect to your computer.

Thus do not use an ADSL modem that connects directly to your computer, although many of the larger Internet service providers give this kind of device away for free.

To safely connect to the Internet you can buy an ADSL modem with a NAT router (often together with a switch and/or wireless access point) for under £50. Many smaller Internet service providers will sell you such a device properly configured. (Several computers and game consoles can connect to the Internet via a single NAT router.)


All computer programs have faults or "bugs" in them. Many faults are minor and most people never even know that they exist, some faults are annoying, and alas some faults are very serious. Some software problems are so serious that they allows someone to connect to your computer without you knowing, and take full control of your computer, and read any file they want, use your computer to commit crimes, and steal all your passwords.

It is vitally important that you keep all your software up to date. Normally when problems are found, the company responsible tries to fix the program, and they often release a fix or "patch", which corrects the broken program. You should check all your software at least once per month: check the web site of the company that created the software and look for notices of new patch releases, download the relevant patches and install them as instructed.

It is important to remember that all software includes Mac OS X, Linux and open-source software, and does not mean just Microseof Windows. People not using Microsoft's software must not automatically feel safe as there have been serious flaws in all software.


Malware is the term used to describe a wide range of computer programs that are designed to damage your computer in some way. Some of them are annoying forms of advert (adware) that you can't get rid of, or something that watches your browsing habits (spyware). They can also be destructive, destroying your files (virus or worm), or stealing your passwords to sensitive web sites like your work or your bank (keylogger and Trojan). Sometimes they are very obvious, some times it's hard to know that they are there - until the damage is done.

Your computer can become infected because you receive an infected disk or email, or because you go to a web site that has been infected, or you can be infected just because you are connected to a network that has an infected computer on - that means both the Internet from home, or via a network at work.

If you run Windows you must obtain a program to help control viruses on your computer. You can buy one, or use a free one, but you must keep it up to date, as new viruses come out daily, and if the anti-virus software doesn't know what to look for it can't find it. You can usually configure your anti-virus program to automatically keep its' self up to date, if not, you will need to visit the web site of the company that created it and download virus definition files and any patches. Keeping your anti-virus software up to date should be a key part of your update routine (see bugs), aim to update your definitions once a week.

When you receive files as email attachments, you should never open them unless you are explicitly expecting them. This is especially true it the email arrives from a friend at Christmas and contains a funny Christmas card, as this is the best way of catching a computer virus.

Contrary to popular opinion, just about any type of file could contain a virus, though in practice many file types are safe. Do not rely on the file extension to decide if a file is safe, it can be easily faked, and could be misleading.

Your Internet Browser

One of the weakest points on your computer is your web browser. By default it is configured for your convenience not your safety, and as such is a very serious security hole in your computer.

Microsoft's Internet Explorer, the default browser for Windows users, and a common browser in use today, is alas the most insecure browser available. It has a number of very serious and unresolved issues that make it so insecure that several governments' security agencies have formally recommended that it not be used.

The best free alternative browser, suitable for most users is the Firefox Browser, by the Mozilla Organization. By default it is not vulnerable to the most severe class of security weaknesses that Internet Explorer is. Additionally, it has many superior features that prevent most of the common nuisances that Internet Explorer users experience, for example pop-up adds and many kinds of spyware are blocked by default.

There are serveral alternative browsers available: Mozilla Firefox being the most popular but there is also Opera Browser, Google Chrome and Apple Safari.

See also Blocking Adverts and Malware and Web Browsers.

Your Email Program

Your email program is another channel for malware to enter your computer. Microsoft's Outlook and Outlook Express email programs use parts of Internet Explorer, and are therefore vulnerable to the same kinds of security problems. Their design also makes you more vulnerable to junk email, commonly called "spam". Even when properly updated and configured, these two programs are not safe, and should be avoided whenever possible.

There are several free alternative email programs, for example the Mozilla Organization's Thunderbird or "Web Mail" via a web browser (e.g. GMail, Yahoo Mail) rather than Outlook.


If you keep all your software up to date, install anti-virus software, do not connect your computer directly to the Internet, never use Internet Explorer or Outlook, and deal responsibly with any files you receive, you should have trouble free computing.


Many high quality programs are available for free download on the Internet. Once you have a high-speed Internet connections they can easily be downloaded in a matter of minutes. The following sites should prove useful: