The Internet is always public, sometimes forever, sometimes prowled by pirates — and sometimes a serious threat to privacy: For example, 

Ashley Madison, you see, is a website claiming 37 million users worldwide that exists to facilitate marital infidelity. According to slightly breathless — and, although I may have been imagining it, also rather worried — coverage across the global press, the site has been bust open by some hackers who are about to release the details of everybody on it. And, on the assumption that those 37 million people actually exist, and aren’t mainly robots, duplicates or outright lies for marketing purposes, I’d say that the ‘bit of a scumbag’ count here must be pretty high. Indeed, I’d say that it covers almost all of them, and the people who made the site, too.
Now, one wonders whether—for reasons such as multiple lawsuits with parties with widely varying interests—this unwanted end-of-all-things revelation will ever happen.
But, that said, many people who might not have been "found out" in the past might now be:  

Joan Bakewell wrote a few years ago of her own long-running affair with Harold Pinter in the 1960s and how, in the more modern age, they simply wouldn’t have got away with it. Itemised phone bills, Facebook, Twitter, internet histories, suspicious new Wi-Fi hotspots popping up on your other half’s phone; all of these things can trip up the unwary. ‘Our plans,’ wrote Bakewell, ‘left no trace.’ When was the last time that was done?

Almost all internet political gaffes are born out of private behaviour suddenly made public. Think of the Tory MP Brooks Newmark emailing an undercover reporter with photographs of himself in paisley pyjamas. Or Jack Dromey, husband of Harriet Harman, appearing to ‘favourite’ explicit gay porn tweets on Twitter (he says it was a technical error). Or, my personal favourite, Gavin Barwell, the Tory MP for Croydon, complaining about an advert to ‘Date Arab Girls’ on a Labour press release without realising that online advertisements are tailored to the user’s internet history. More. 
User internet history may be a damaging and unfair source too. As noted earlier, big companies spy our every move on the internet. Yet the targeted user may be engaged in a lawful activity exploited by pressure groups aided by government. I trust readers to assume that I hold no brief whatever for adultery. But a serious question arises: How much good will such invasions of privacy do?
A question that will be revisited many times, I suspect. See also: Helping teens stay real in the world of virtual: Reputation management Rise of Big Data The Sony hack: How the Internet changes the balance of power, Part II Hollywood, despite bravado, buckled

Denyse O’Leary is a Canadian journalist, author, and blogger.