There really is no yes or no answer "per say"...
Hollywood has sneakily made a difference between the words based and inspired. Apparently, inspired is made up while based on is truly based on a true story. The Strangers was a great movie in my opinion however, it was "inspired by a true story". The Strangers was loosely based on various home invasion murders, including The Manson Murders, and based upon an Austrian couple that was murdered by three teenagers in their vacation home in The Czech Republic.
The True Story Behind the New Movie "The Strangers" is a mixture of three stories.
The killers, a principle male assailant and female accomplices, is based upon Charles Manson and the Manson killings.
The frantic "there's blood everywhere" 911 phone call and "bounding to a chair and stabbing" was based on the killings in Cabin 28.
The basic story of a couple being terrorized by a group of people was based on the famous killing in the Czech Republic, which was also made into a French Film titled Ils, translated to mean "Them."
In the Czech Republic murders, an Austrian couple are terrorized in their vacation home by three teenagers and are later killed in the forest when they try to escape. BUT, a concrete source for this alleged crime has yet to be found other than countless blog postings, leading most people to believe that the story was engineered much like the Blair Witch Project, to give Directors a legal excuse to claim that it was based on a "True Story."
In the Cabin 28 murders, the daughter of a woman walks into a cabin where her mother, brother, and brother's female friend were staying only to find them stabbed and hammered to death. She calls 911 frantically repeating "there's blood everywhere," which there was although no one heard anything all night.
This took a few hours to finally piece together, but I noticed that no one else had figured it out and wanted to be the first to say, "I cracked the story."
So in the end The Strangers inspired by aTrue Story claim is definitely true, but a combination of several stories to appeal to general audiences. That's Hollywood, but, as scary as it may be, also real life.
(By the Way...Bryan Bertino...the writer and director admitted to this.)
hope this helps:) much love xoxo