Tesco's admission that it still merrily emails passwords to punters in plain text has alarmed anyone with a grasp of computer security.

The UK's supermarket behemoth reassured the world on Sunday that it stores passwords for online shopping accounts in an encrypted format, and only decrypts them when users forget their login credentials and request a reminder via email.

This cut little ice with many Reg readers, who contacted us in large numbers on Monday morning. They pointed out that the method is undesirable because it fails to meet the security industry's best practices. It would be far better if Tesco switched to a secure password reset process with salted hashes for users' login credentials.

One (unlikely) danger is that these unencrypted email password reminders could be intercepted and used by crooks. But the bigger issue is that the method implies that the grocer stores passwords in a way that could allow anyone who infiltrates the website to uncover the original plaintext credentials: if Tesco can decrypt stored passwords for reminder emails, hackers can too.

The password reminder issue was raised again at the weekend by developer Troy Hunt but the same issue was actually first reported five years ago, back in 2007.

It's poor practice to send out password reminders in the clear-text but Tesco is hardly alone in this, and it's hardly the most wretched of security sins. The tone and severity of criticism against Tesco would be justified had its systems had actually been hacked and the passwords exposed - as has happened to other and still more prominent organisations in recent times - but this doesn't appear to be the case.

The password reminder issue is just the most obvious in a security of security mistakes by the grocer, according to Hunt, who list the various flubs in a blog post here. Other problems include using unencrypted authentication cookies and mixing up encrypted and unencrypted content on a secure page, behaviour that likely to generate browser warnings that most users will find confusing. For good measure Tesco's website is insecurely configured and running IIS 6, a seven-year-old and twice superseded version of Microsoft's web server software.

We asked Tesco for a more substantive response covering these various concerns but at the time of posting we're yet to hear back from the retailer. We'll update this story as and when we hear more. ®