Stay one step ahead of the fraudsters with our series of articles giving you the lowdown on the scams they use to trick people out of their hard-earned cash - and how to avoid being taken in by them.
This week, we focus on a new computer virus scam involving bogus British Gas bills.
How does it work?
Hundreds of thousands of people are being targeted with a crafty new scam in which criminals email them fake British Gas bills designed to persuade them to download a "Trojan horse" virus on to their computers.
Titled "Your summer gas & electricity bill", the dodgy emails are sent from a genuine-looking address and use the company's branding.
However, anyone who clicks on the link to view their bill is told to download a file that contains the virus.
Once their computer is infected, they are then "locked out" and told they must pay an online ransom to get back in.
How can I avoid being caught out?
A number of businesses, schools and hospitals - as well as lots of consumers - have been taken in by this devious "ransomware" scam.
To avoid joining them, you should call British Gas to check that any email bills you receive are genuine before clicking on any links within the message.
And treat any emails that are not addressed to you by name with particular caution. Genuine email from British Gas will always be addressed to individual customers and will include their account numbers.
I've been defrauded. What should I do?
If you receive a dodgy email purporting to be from British Gas, forward them on to the company, which is doing its best to stop those responsible.
British Gas said: "Any customer who is concerned about a phishing email can forward it to firstname.lastname@example.org."
If you have been locked out of your computer by ransomware, meanwhile, you can remove it by stripping it of all the files and software previously installed and resetting it to what is called factory condition.
It's a pain, but you can reinstall the files and software from your back up system if you have one, and it allows you to avoid paying the criminals.