With the UK heatwave expected to increase temperatures over the next week, you decide to invest in an air conditioning unit. But they are expensive, and stocks are running out in the shops as everyone else has had the same idea.

After a quick search, you see that there are other options online, and some from names that you recognise.

Aldi seems to have a good deal – an air conditioner unit at just one-third of the normal price. As the heat builds up, you pay for one.

Only too late do you discover that you’ve visited an elaborate copy of the real Aldi website, and handed your card details over to criminals.

By claiming to offer huge discounts on sought-after goods, criminals are hoping that their victims will act quickly and without much thought. With low stocks at genuine retailers, combined with record temperatures, people are acting in the heat of the moment.

Aldi is not the only retailer being used in this way, although of the examples seen by Guardian Money it was the best-known brand.

Olga Altukhova of the cybersecurity company Kaspersky, which uncovered the fake sites, said pressuring buyers to act quickly is one of the techniques criminals use.

“When demand spikes, warnings that only a few items are left or that a discount is about to expire can easily compel users to enter financial details or personal data,” she says.

What it looks like

The fake Aldi website highlighted by Kaspersky is a sophisticated replica of a real site from the retailer. Kaspersky warns against opening links on emails that may lead you to such sites.

One ad on the fake site lists an “energy efficient” air conditioner and heater set for £28.13, down from £64.44. “Only five left in stock,” it says.

Another ad lists a “3-in-1” portable air conditioner with dehumidifier for £149.99 – a fraction of the £474.99 the fake site claims the product usually retails for. Just 11 units are left in stock, it says.

The site aims to fool people by using the Aldi logo and real products on its pages, says Kaspersky. It will typically display the number of visitors viewing the product and set a time limit for when you can buy at the special price.

What to do

As with any potential purchase that looks like you are getting a bargain, be sure to stop and think. Large amounts of money off – especially when items are in demand – and limited times to buy are red flags that you are on a fake site.

“To avoid falling victim to such scams, stay calm and double‑check everything, especially the website’s URL and design,” says Altukhova. “If you’re unsure about a site’s authenticity, look it up in a search engine to verify it’s legitimate, or use a security software to perform the check.”

Aldi says it tries to identify and report fake websites. It said genuine offers are only available though its official site and social media accounts.

If you find that you have given out your financial details, contact your bank and Report Fraud and then change your passwords.