By Mark Ward
Technology correspondent, BBC News website
If your house was burgled only 12 minutes after you moved in, you would probably think about selling up and moving on pretty quickly.
Do you know if viruses or spyware are lurking on your machine
While this may not happen to your home, it will happen to the PC you use to browse the web if you do not have anti-virus software or a firewall installed.
There are so many malicious programs prowling the web that there is a 50% chance that a vulnerable Windows machine will be found and compromised after just 12 minutes online.
Even if your home computer is protected, every time you go online those worms and scanning programs will be rattling the digital locks to see if all the loopholes are closed.
Home PC security has never been more important, especially now that more people in the UK use broadband than dial-up to go online. High-speed connections means people spend more time online and are attacked more often.
As Britain's net using population grows from the 52% of households currently online, increasing numbers of homes have more than one PC and many are poorly protected.
"Up to 40% of home users do not have any anti-virus software on their computers," says Peter Craig, spokesman for Trend Micro, which makes anti-virus software.
This can put confidential information at risk says Mr Craig, given that increasing numbers of people bank and shop online.
What people need to protect themselves against has grown too with spyware, spam and phishing attacks joining the list of hi-tech threats.
At the most basic home, PCs need to have a firewall, anti-virus and anti-spyware software in place. These programs need to be regularly updated and the machine should be scanned at least once a week to ensure no nasties have crept on to it.
Part of the reason for this poor protection is cost. To be safe, every computer in a home network needs to have a full suite of security software installed. The quickly multiplying cost can make many balk and cut corners.
But steadily security companies are waking up to the fact that many households are networked and have several PCs in use.
"We're starting to offer three-user home network editions," says Nick Bowman from security firm McAfee.
Home networks are getting easier to set up
Trend Micro, Kaspersky, CA, McAfee and others all have multi-user versions. Where they differ, apart from in cost, is in the way the software is updated.
Some force every machine to be treated individually. This can be time-consuming if it has firewall, anti-virus and anti-spyware products installed.
Most anti-virus programs come with an auto-update option. It can be worth turning this on just to ensure the latest protections are downloaded as soon as they become available.
Threats emerge so fast that some anti-virus companies release updates hourly.
Others are starting to introduce tools to make this updating job even easier.
"You can have a master copy of PC Cillin that makes sure all your copies are up to date just by clicking on one," says Mr Craig from Trend Micro.
Similarly Kaspersky Labs' anti-virus software lets one copy update itself via the net and then copies on other PC can download updates from that machine via the home network.
But, says Mr Bowman from McAfee, the tools that people can use to keep security software up to date are evolving all the time.
"It's a classic example of a maturing market," he says. "It's not quite yet got to the stage of having network administrators in the home."