Consumers have been urged to exercise caution when shopping online this year, as not all ads may be quite what they seem.

With many shoppers looking to avoid the crowds, it’s little wonder they spend millions of pounds at online stores each day in the run-up to Christmas. However, it’s not only retailers that want consumers to part with their cash, but scammers too. What’s more, by including their ads on legitimate websites, cyber criminals are hoping to take on a little extra credibility by proxy.

Cyber criminals have been found to use authoritative online retailers to place their scam ads. Then, any users who click through will unwittingly kick-start a malware download.

At its most dangerous, this malware can log keystrokes, so the criminal knows exactly what a user is typing in to web dialog boxes. Armed with this information, the crooks can then glean passwords that could grant access to all manner of accounts – be it email, social networks or even online banking.

Others, meanwhile, have been found to go down the ransomware route, where they lock a device then demand money for its ‘safe’ return. However, in many cases the ransomware is so shoddily made that even after a user’s files have been restored the system is scrambled to such an extent that the files are largely unusable anyway.

Though most of these fraudulent ads would require users to click through in order to inadvertently download the malware, some are more dangerous still – as they don’t require such action.

As Bentley University professor Steve Weisman told Turn to 10: “You’re probably thinking, ‘I never click those ads, so I’m safe, right?’ That’s not even enough.

“There are scammers that will infect certain ads, and what they do then is they infect these with a type of malware that will infect the entire legitimate website that you go to.”

Weisman went on to recommend not just using a comprehensive and up-to-date antivirus programme, but also anti-adware, too. Such software, he said, will screen out all ads and protect users from scams like these.