The Information Commissioner's Office (ICO) has published a report detailing the most glaring security failings it has encountered in its investigations.
It said that fines as large as £250,000 were levied against large companies over mistakes that could have easily been avoided.
Eight common vulnerabilities make its list and the ICO said that the incidents ran up fines that totalled £1m (PDF). The eight most common issues seem obvious, but are often overlooked, the watchdog said.
They include a lack of encryption, poor password protection, a lack of up-to-date software, bad design, SQL injection vulnerabilities, and a reliance on default information, including logins.
The ICO's group manager for technology, Simon Rice, said organisations have reacted to some complex issues but have missed other key areas that can be tackled easily.
"In just the past couple of months we have already seen widespread concern over the expiry of support for Microsoft XP and the uncovering of the security flaw known as Heartbleed. While these security issues may seem complex, it is important that organisations of all sizes have a basic understanding of these types of threats and know what action they need to take to make sure their computer systems are keeping customers' information secure," he said.
"Our experiences investigating data breaches on a daily basis shows that whilst some organisations are taking IT security seriously, too many are failing at the basics.
"If you're responsible for the security of your organisation's information and you think salt is just something you put on your chips, rather than a method for protecting your passwords, then our report is for you."
Recent fines issued after ICO investigations include the £200,000 awarded against the British Pregnancy Advice Service and a quarter of a million pound fine that Sony received following breaches on its networks.
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