Computers, phones and webcams that are connected to the internet suffer an attempted cyber-attack every five minutes, according to new research.

A report by the cybersecurity firm Netscout found that it took that long on average before a device which was newly connected to the internet experienced a "doorknob-rattling" attempt to break in.

These attacks were the same kind used by Mirai, a malicious program that caused chaos in 2016 by taking over more than 600,000 devices and using them to launch denial-of-service attacks on websites including Netflix, Airbnb and Twitter.

Most computers and smartphones would be immune to such methods, but numerous so-called "internet of things" devices such as webcams, digital video recorders and printers remain vulnerable.

"If you take your laptop into a coffee shop, and you have a public IP address, the chances are that someone is going tor try," said Matt Bing, principal security analyst at Netscout.

"In the last 24 hours we saw over 20,000 attempts to log in, and that's just one day.... this activity is kind of like the background noise of the internet. It's just always there."

The report illuminates how "botnets", swarms of malicious devices that have been infected with malware and now seek to infect others, have become a permanent feature of the online world.