What the media have called Britain's "cookie law" became enforceable this weekend and will require UK-based website operators to give visitors notification if the website will use any method of tracking—not just cookies but other types of analytics as well—on the user's computer.

The law is the UK's version of a larger "e-privacy directive" ordered by the European Union. While the date for this law to go into effect has been on the books for a year, the BBC says that most websites will not be in compliance by this weekend, and even the British government isn't quite up to speed yet. "Last week the government admitted that most of its sites would not comply with the new rules in time," the BBC reported. "It said it was 'working to achieve compliance at the earliest possible date.'"

Most Ars readers will know that cookies are commonplace on the Internet. Websites that want to tailor ad-space to their users, or want to save a user's viewing preferences for the next session, or want to keep items in a user's shopping cart as they navigate away from checkout to find more items, will all require the use of cookies saved on that user's computer. But a backlash against tracking cookies, especially from third-party clients that can store a user's browsing history for long periods of time, spurred the British government to require consent when tracking methods are used on websites based in Britain.

Eventually, the British Information Commissioner's Office will charge fines of up to £500,000 for non-compliance with the cookie laws, but at the moment it seems to be downplaying punishment in favor of educating non-conforming site admins.

Still, the ICO is doing itself no favors when it comes to clear directions on implementation. Just days before the law was set to become official, the office modified its message, saying that 'implied consent'—or continued use of a website or application by the user who has been shown a message about the use of cookies—would be adequate in complying with the law.

Note: This story has been updated to include mention of the EU's broader cookie law.