Treating email attachments with suspicion used to be #1, but after the NIMDA worm the rules have changed.

Many programs, and particularly anything produced by Microsoft, are riddled with security holes when they are released. Effectively the public are used as the last step in testing a product (which is cheaper than rigorously testing in-house prior to release). Whenever a security issue comes to light, the software maker issues an update or a patch. By issuing the patch, they are also alerting the wrong-doers to the vulnerability of unpatched systems. The result is that today a pristine installation of, say Windows 98 and Internet Explorer 5 is unprotected from a number of known and well-publicised methods of attack.

One particularly alarming security hole in Internet Explorer allows Email attachments to be executed automatically. This has been exploited by a number of viruses, the most widespread and most damaging being the recent NIMDA worm. Had you received it, as millions did, on the day of its release (and therefore before any anti-virus programme could recognise it), caution about opening e-mail attachments and virus-protection would not have saved you if you hadn't installed the relevant patch. So keeping your patches up-to-date is now #1 on my list of essential security measures.

There is one essential and easy to use FREEWARE tool - Big Fix - which will check for available patches and scan your system to check which ones you need. Not only does BigFix check your update needs, but it can alert you to, and help you fix, some other potential problems on your system. But note that BigFix is not 100% reliable and should really be used in conjunction with (and not instead of) other measures.

As well as Microsoft's own Windows Update and (for Office users) Office Update services, which require ActiveX and even then sometimes don't work, you can download patch installation files directly (for archiving or network installation) from Microsoft Download Center: Windows (Security & Updates) and Microsoft Office 2002 Download Center.

Viruses have now become so widespread, and so sophisticated that avoiding coming into contact with them is now impossible. You may have your system patched and you may know not to open attachments, but does everyone else who uses your computer/network? In the slow old days, when running an anti-virus programme in the background noticeably affected the performance of your machine, the choice to turn automatic virus protection off was sometimes the only way to get any work done. But now it is just foolishness.

Most anti-virus software works by detecting viral 'signatures' - the bits of code which are unique to each virus. When scanning for known viruses they refer to a database of signature definitions. Since new viruses are released every day this database must be updated regularly. The most prevalent viruses tend to be recent releases which catch out users who think they are protected just because they are running anti-virus software but who haven't updated the signature definitions recently enough.

Get a good anti-virus programme(Grisoft's AVG Anti Virus) and configure it to (at least) scan every file as it is created or downloaded.

Update your virus signatures regularly. You'll know if this is happening, because it generally means downloading and then running a file. Generally it is recommended that you do this at least once a week, and certainly you should do it at least once a month, no matter how much you use the 'net. If you set up your protection to be always on, your antivirus program *should* remind you when your signatures need updating. If (as I recommend below) you subscribe to a virus alert newsletter, you might also choose to update your signatures when there is any outbreak of a rapidly spreading new virus.

This used to be the first rule of email, and you should already know this. The vast majority of viruses arrive as attachments to emails. Most of them are harmless until they are opened - (UNLESS you are not diligent in keeping your patches up-to-date in which case you may be vulnerable to a flaw in Internet Explorer which allows Email attachments to be executed automatically; see Microsoft Security Bulletin (MS01-020) for details of this vulnerability).

Do not trust any attachment to be what it claims to be or the message it comes with claims it to be. All of the information in the header of the email, including the identity of the sender, can be forged and the true identity of the attached file may also be disguised, so until you have scanned them and are sure they are safe it is best to treat ALL incoming attachments as suspicious.

Do not trust an email to be from who it says it's from. Most viruses spread by automatically (and invisibly) forwarding themselves to addresses they find in the address book or in messages stored in the inbox of an infected machine, so you CANNOT assume that just because a message (says it) comes from a friend it is innocent. Even 'innocent' files which you are expecting from known senders may be infected either by a virus residing unidentified in their machine or even (theoretically) en route.

1. NEVER OPEN ANY ATTACHMENTS without scanning them for viruses first.

2. NEVER OPEN ANY ATTACHMENTS unless you are expecting them, know who they're from and have scanned them for viruses first. If you are in doubt, do not open the attachment - contact the sender asking them to confirm what they have sent you (and why).

3. NEVER OPEN ANY ATTACHMENTS directly from within your email client. Always save attachments to disk first and then scan them before opening them. It is best not to assume that your virus scanner is set up to scan incoming email correctly. Doing it manually, so you can see that it is working, is the safest way.

4. Avoid opening .doc files in Word. Always use a file viewer or WordPad to read files with a .doc extension. If you want to keep the file, start up Word and then copy and paste the contents of the attachment from the viewer to a new .doc. (see also Sending (Word) .DOC attachments below).

5. Set up 2 filters to put all incoming mail with attachments and all suspected spam containing attachments into 2 separate folders. Doing so will not actually make you more secure, but it will be easier for you to remember to be extra cautious when dealing with any messages in those folders. (For details of how to create these filters see Spam fighting)

Download and install a personal firewall such as Zonealarm or Agnitum Outpost. In tests these FREEWARE personal firewalls have proved more effective than some big name commercial ones.

Immediately after installing your firewall you may be frustrated to find you can no longer connect to the 'net - not using your browser, not using your email client - not with anything. This is good - it means the firewall is working exactly how it should. When any app tries to connect, you decide whether to allow it or block it. After a while all your regular programs will be allowed, and you will only be alerted when something new tries to connect.