PARIS — In the digital world, the most effective advertising is not always advertising in the traditional sense. Instead of buying ad space or time on a Web site, many marketers prefer to build their own sites or mobile applications or to promote their brands using social media, encouraging consumers to spread the word.

While some of this activity remains unregulated, prompting concerns that the Internet is a haven for misleading or unscrupulous marketing, with brand owners doing things they would not dream of doing offline, the loopholes that allow this double standard are slowly closing.

Last week, the Advertising Standards Authority of Britain, which monitors the content of most forms of advertising in that country, including paid Web ads like banners and sponsored search links, provided details of a plan to extend its oversight to social media, company Web sites and other nontraditional digital marketing activities. That means advertisers could run afoul of the standards authority for a misleading blog post or even a consumer’s Twitter postings, if they were part of a campaign employing user-generated content.

The British regulator was not the first to do this. The standards police in more than a dozen other European countries had already extended their monitoring to cover new kinds of marketing, after pressure from the European Commission in Brussels. In the United States, the Federal Trade Commission recently published guidelines for marketing via social media and blogs.