Action Fraud has received reports from businesses across the UK that have been emailed to be told they will be under cyber-attack if they don't pay up hundreds of pounds.

The scammers, who have been calling themselves 'RepKiller Team' (although that can quickly change, warns Action Fraud), have been sending emails to businesses demanding payment of between £300 and £500 in Bitcoins, an internet currency, by a certain date and time.

If the demands are not met, the RepKillers threaten to launch a cyber attack against the businesses, putting hundreds of negative reviews online. As the sums being demanded are relatively small, some companies have paid up rather than risk not doing so. But once a company has paid it often receives further threats.

The emails also claim that once actions have started, they cannot be stopped.

What to do if you receive one of these emails

• Whether the attack is attempted or successful, you should report it to Action Fraud on 0300 123 2040 or by using the online reporting tool at www.actionfraud.police.uk/report_fraud
• Do not pay anything. The threat may or may not be real, but paying will not guarantee you are not attacked and will probably lead to further demands for money. 
• Retain all the emails. Should law enforcement investigate, the information contained in the email headers can be used as evidence.
• Maintain a timeline of the attack, recording all times, type and content of contact.