Google has defended the length of time it retains web-users' data following the release of a report on the way European data-protection laws should be applied to Web-search services.

In its report, which was published last week, the Article 29 Working Party recommended that search services should be doing more to protect Web users' data. Failing to do so may be viewed as unlawful, according to the report.

"It is the opinion of the Working Party that search engines, in their role as collectors of user data, have so far insufficiently explained the nature and purpose of their operations to the users of their services," the report states.

"The Working Party does not see a basis for a retention period [for user data] beyond six months," the study concludes.