Police are urging computer users to be on their guard against a nationwide scam in which fraudsters are spamming fake British Gas bills.
The fraudsters are sending the fake emails out that look like a genuine gas bill. There is a link on it which, if clicked on, installs ransomware on to the computer.
The ransomware then locks the computer and the fraudsters then demand money to unlock it.
Detective Inspector Benn Kemp of West Yorkshire Police's Cyber Crime Team, said:
"This is a nationwide fraud that we are aware of and I would urge people to be on their guard. I would ask people to never open an email unless they are certain of the credentials of the sender and to share our message with other people.
"British Gas for example always send personal emails and will usually quote the customer's account number. Their links are always www.britishgas.co.uk.
"You should also regularly update your anti virus and browsers, avoid public wifi connections when doing things like internet banking and back up all your files."

Subway Robber Jailed After Attacking Employee in Slough
Four Sentenced Over £15,000 Cannabis Supply in Accrington
Leeds Secures £1m for New West Yorkshire Veterans Support Hub
Bradford Teen Jailed After Police Chase Leaves Five Injured
Man Arrested After Teenager Injured in Yiewsley Knife Attack
Man Jailed for Damaging Charity Elephant Statue in Slough
Bradford Drug Dealers Jailed After £22,000 Drugs Seizure
Bradford University Theatre to Close After 50 Years
Woman Shot Dead in Feltham Named as Man Charged with Murder
Rochdale Drug Gang Member Jailed for More Than 10 Years
£6m Leeds Road Safety Scheme Begins with Lane Closures
Twelve Men Arrested in Kirklees Historical Child Abuse Investigation
Remix Saturdays
Bhangra Nights
Legal Show
The Golden Era