Thousands of websites in Europe are expected to be in breach of a law that dictates what they can log about visitors.

European laws that define what details sites can record in text files called cookies come into force on 26 May.

Cookies are widely used to customize what repeat visitors see on a site and by advertisers to track users online.

The Information Commissioner’s Office (ICO) said it would offer help to non-compliant sites rather than take legal action against them.

The regulations say websites must get “informed consent” from users before they record any detailed information in the cookies they store on visitors’ computers.

Among websites that have complied with the law, getting consent has involved a pop-up box that explains the changes. Users are then asked to click to consent to having information recorded and told what will happen if they refuse.

Thousands of websites in Europe are expected to be in breach of a law that dictates what they can log about visitors

The ICO has also updated its policy to allow organizations to use “implied consent” to comply. This means users do not have to make an explicit choice. Instead, their continued use of a site would be taken to mean they are happy for information to be gathered.

However, it was a “concern” for the ICO that so many sites were not yet compliant, said Dave Evans, group manager at the ICO who has led its work on cookies in the last 18 months. However, he added, it was not necessarily easy for companies to comply with the laws because of the amount of work it involved.

On busy sites, he said, an audit of current cookie practices could take time because of the sheer number of cookie files they regularly issue, monitor and update.

Dave Evans said the ICO was expecting sites that were not compliant to be able to demonstrate what work they had done in the last year to get ready.

Fines for non-compliance were unlikely to be levied, he said, because there was little risk that a non-compliant site would cause a serious breach of data protection laws that was likely to cause substantial damage and distress to a user.

It was planning to use formal undertakings or enforcement notices to make sites take action, he said.

“Those are setting out the steps we think they need to take in order to become compliant and when we expect them to be taking those steps,” he said.

“If they comply with one of those notices or sign one of those undertakings they are committing to doing this properly and that’s the main point.”

As well as advising firms, the ICO has also issued guidance to the public that explains what cookies are, how to change cookie settings and how to complain if they are worried about a site’s policy.