Nearly 20 per cent of adults polled confessed they never change their passwords, with 15 per cent saying they only did once every two years.
A staggering eight per cent of 2,000 Brits polled admitted to using their own name as their password with 14 per cent using their pet's name.
The study, commissioned by gadget insurance provider Row.co.uk, also found that 16 per cent admitted to using the same password for every account.
More than half of those polled (55 per cent) said they chopped and changed between a small list of passwords with just 29 per cent using a different password for every account.
Over a quarter of people are still writing passwords down on a piece of paper.
The study follows research by security and productivity software firm SplashData earlier this year, which revealed the worst passwords of 2015 based on data from more than two million leaked passwords.
Top of the list was "123456", followed by "password", "12345678", "qwerty" and "12345".
The latest study comes after hackers raided personal information associated with over 500,000 Yahoo accounts.
The information included people's names, email addresses, phone numbers, dates of birth, hashed passwords and encrypted or unencrypted security questions and answers.
Overall, the study found that middle-aged Brits were surprisingly more security-savvy when surfing the web than their own children.
The over-55s are more likely to use a different password for each account they hold than young adults.
More than a third (35 per cent) of over-55s use separate passwords compared to just 19 per cent of 18-24 year olds, according to a survey of 2,000 computer users.
The over-55s also chose passwords that are harder to guess, with 70 per cent of them saying they never use their name, pet's name or partner's name in a password.
Just one per cent of them admitted to using "password" as their password, compared with seven per cent of 18-24-year-olds.
The over-55s were also more likely to back up their financial records (23 per cent) than the younger generation, with just 10 per cent of 18-24-year-olds doing so.
They also chose more old-fashioned methods to remember a password, with 37 per cent preferring to write it down, compared with 20 per cent of 18-24-year-olds.
And they were the least likely generation to save their password on a device - unlike 13 per cent of 18-24-year-olds.
Eleven per cent of this young age group actually used a password manager app to keep track of their passwords.
Richard Waters from Row.co.uk said: "Amidst the hacking of a number of popular online platforms in recent times, having a secure password has become more important than ever.
"Our study has made it clear that the younger generations have less of a regard to password security than those senior to them. With these age groups more likely to have more online accounts and being less likely to use a variation of passwords, they're leaving themselves prone to hackers."
A total of 2,000 adults from around the country took part in the survey, which was carried out in September this year.