Two in three hotel websites leak guest booking details and allow access to their personal data to third-party sites such as advertisers and analytics companies, a new report by California-headquartered global cybersecurity company Symantec said on Thursday.

"I tested multiple websites, including more than 1,500 hotels in 54 countries, to determine how common this privacy issue is. I found that two in three or 67 per cent of these sites are inadvertently leaking booking reference codes to third-party sites such as advertisers and analytics companies," Candid Wueest, Principal Threat Researcher, Symantec, said in a statement.

All of the hotels did have a privacy policy but none of them mentioned this behaviour explicitly.

Notably, it has been almost a year since the General Data Protection Regulation (GDPR) came into effect in Europe, but many hotels affected by this issue have been very slow to acknowledge, much less address it.

However, some reservation systems were commendable as they only revealed a numerical value and the date of the stay and did not divulge any personal information. But a majority of them leaked personal data including full name, email address, postal address, mobile phone number, last four digits of credit card, card type and expiration date, and passport number.

Over half (57 per cent) of the sites that were tested send a confirmation email to customers with a direct access link to their booking. This is provided for the convenience of the customer, thus, allowing them to simply click on the link and go straight to their reservation without having to log in.

"Since the email requires a static link, HTTP POST web requests are not really an option, meaning the booking reference code and the email are passed as arguments in the URL itself.

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"On its own, this would not be an issue. However, many sites directly load additional content on the same website, such as advertisements. This means that direct access is shared either directly with other resources or indirectly through the referrer field in the HTTP request," Wueest noted.

"My tests have shown that an average of 176 requests are generated per booking, although not all these requests contain the booking details. This number indicates that the booking data could be shared quite widely," he added. (IANS)