Is my computer safe from outside attack when it is in Sleep mode?

Q  I have a basic desktop computer running Windows XP. Can you advise me about the security of my computer if I use the Sleep mode instead of shutting down and switching it off at the mains?

For example, if my computer is in Sleep mode will my AVG anti-virus software and other updates still be downloaded onto the PC? I use BT’s broadband service via a Home Hub, which remains connected and powered at all times.

I am particularly concerned about someone gaining access to my internet banking details and passwords and so on.
Terry Jobling

A  When a Windows computer is placed into Sleep mode, it essentially enters a low-power state in which it does nothing. In fact, pretty much all that happens is that power continues to be supplied to the PC’s memory, so that any programs or open documents are not forgotten and can be quickly displayed when the user commands the computer to wake from Sleep.

As such, the most direct answer to your question about updates is no – nothing will be downloaded when a Windows PC is in Sleep mode. This isn’t a problem, because such updates can (and typically do) happen in the background, when the PC is being used normally.

However, your secondary question raises some interesting security concerns that we think are worth addressing. Many modern computers (or rather, their network adapters) have a feature called ‘Wake on Lan’ or ‘WoL’ that enables someone to wake a PC remotely.

The Lan part of this stands for ‘local-area network’ and this essentially means that the ‘remote’ command to wake the PC must be performed on a computer connected to the same network.

This won’t give outsiders access to the PC, incidentally: it merely wakes it up from Sleep (or even from off, though not if switched off at the mains).

We should also say that there is a theoretical risk that the WoL command could come from the outside world (ie the internet), but as well as being extremely unlikely, with a firewall in place this doesn’t pose any threat.

The BT Home Hub has a built-in firewall (refer to the instruction manual if you wish to use it), and the Windows Firewall should be enabled by default. If you want to check, in XP click Start followed by Control Panel, then Security Center and finally Windows Firewall. Ensure the On radio button is selected and click OK.

If Wake on Lan technology bothers you, it is possible to disable it. In XP, click Start, right-click My Computer and choose Properties. Now select the Hardware tab and click the Device Manager button.

In Device Manager, click the plus (‘+’) symbol next to Network Adapters to expand the category, right-click the relevant network card and choose Properties. Choose the Advanced tab and look in the Property list for an option called ‘Wake on Lan’, ‘Wake on Magic Packet’ or similar, click to select it and then choose Disabled. Click OK to close the dialogue box.

Finally, as another layer of defence, make sure your user account is protected by a password. In XP, click Start followed by Control Panel and click User Accounts. Now click the Change an account link, click the account name, click Change my password and follow the prompts.