The Internet loves a good mystery. From cracking complicated codes to identifying obscure songs, web users love to solve the unsolvable.

Online communities such as Reddit and 4chan have entire threads devoted to picking apart riddles, while sites like Websleuths are created solely for the purpose of crime-solving.

See also: 6 Obscure NASA Sites Every Nerd Has to See

Though Internet detectives have sometimes gone too far (Redditors incorrectly identifying the Boston Marathon bomber, for example), there are quite a few times they've actually cracked the case.

From aiding investigations to saving lives, here are seven examples of Internet users banding together to solve a mystery.

1. Decoding a dying grandmother's writings

Image: Flickr, Linus

When an elderly woman named Dorothy Holm was dying of cancer and her mental health began declining, she started to write scrambled letters onto index cards. Confused, her granddaughter, Janna, posted photos of the cards on Ask MetaFilter, asking users to help her decode the garbled letters. Comments quickly flooded in, with people quickly unscrambling the letters as the Lord's Prayer.

One index card started with "OFWAIH," which commenters decoded as an acronym for: "Our father who art in heaven." The mystery had been plaguing Janna for 20 years, but the Internet solved it in 13 minutes.

2. The Reddit Bureau of Investigation

Image: Flickr, Jonathan McIntosh

When Redditor and college student shadybusiness15 took apart one of his extension cords, he noticed something wasn't quite right. There were mysterious wires and a SIM card with a serial number in it. Curious, he posted photos of it to the subreddit The Reddit Bureau of Investigation, a thread for Redditors who are passionate about solving mysteries.

Users quickly identified the mysterious parts as audio surveillance. The contraption connected to a phone number, which the owner could call to pick up audio in his room at college. Shadybusiness15 called the number and found out it was now disconnected. Some shady business indeed.

3. Zelda's impossible, ancient language

Image: Flickr, Colony of Gamers

In the Zelda video game series, characters use a made up language called Hylian. Nintendo, the game's creator, usually issues a translated alphabet for the game, but changed its mind for the 2011 release The Legend of Zelda: Skyward Sword, claiming it was impossible to translate.

That didn't sit well with fans, who immediately set out on forums to crack the language. Though they nearly decoded it, users kept getting stuck on J, Q and X — except for Sarinilli Morian. The Zelda fan figured out that if you broke the alphabet down into certain patterns, then paired the pattern up with a smaller sign within the game, you could figure out the whole alphabet. Zelda fans of the world rejoiced.

4. Identity of a 35-year-old corpse

A 25-year-old woman named Paulette Jaster mysteriously went missing from a Michigan town in 1979, putting her family on the road to a decades-long search for her.

In 2014, forensic anthropologist Sharon Derrick was attempting to identify a body that had been buried in a pauper's grave in Texas for 35 years. The two didn't seem connected, until Derrick received a random tip from someone on the Internet, who had put together the similarities between the cases (the U.S. Department of Justice runs a web database called NamUs, which lists info on unidentified bodies and attempts to identify as many as possible).

Once Derrick received the tip, she was quickly able to confirm it, thus ending the family's journey for the truth.

5. The time-traveling woman in a Charlie Chaplin film

In the 1928 film The Circus, starring Charlie Chaplin, a woman looks like she's holding and talking into a cellphone. Naturally, the Internet ran rampant with time-traveling and conspiracy theories. But a simple YouTube comment busted through that.

User Crennycrenshaw commented on this video with a simple explanation: "Go to the Siemens hearing aid website then click the link to view their history of hearing aids. The 1924 model has a picture that illustrates how it was held and it explains this mystery." The woman was likely just holding and testing out a hearing aid, not jabbering away on an iPhone.

6. The anonymous Tumblr teen contemplating suicide

Image: Flickr, Romain Toornier

Anonymity on the Internet is a double-edged sword. Jackie Rosas, an 18-year-old teen in California, had been following a mysterious Tumblr account for about a year. It belonged to a 16-year-old girl, who had written posts "laced with depression." Rosas noted the threats, but was taken aback one night when the girl posted that she was was going to end her life.

Despite not knowing the girl's identity, Rosas jumped into action, calling a suicide hotline and then the police. But the only information she had was the girl's first name — no last name, no location, no description.

Digging through her Tumblr account, Rosas, the police and a local high school principal named Karen Dimick worked together, eventually finding the girl's Twitter page. From there, they dug through her tweets, gleaning her last name, location and high school.

The search took a whopping eight hours, but saved the girl's life. Police found her at home, where she had a taken a dangerous amount of pills, and immediately whisked her to a medical facility.

7. A song so obscure you've probably never heard of it

It's happened to you before. You hear a sliver of a song, it gets stuck in your head and you turn to the web to find out what it is. But what if the song is so obscure that even the Internet doesn't know?

That was the case with a new wave song from the '80s that nobody could identify. Dubbed "Stay (The Second Time Around)" by fans, the song had been ruminating on message boards and Reddit, and kept stumping people. Recorded from a German radio station in either 1984 or 1986, the song's origin was muddied and lost in time.

But in 2013, a Redditor named Stefan, who worked for a Swedish radio show, recognized the song, revealing that it was by an artist named Johan Lindell. The show interviewed Lindell, discovering that "Stay" was really called "Up On the Roof," and was from his 1985 album Ghost Rider. Why didn't Lindell step forward earlier? He's not really tapped in.

"...I never visit the internet and I hardly use [the] computer,” he said in the interview.

Oh, how things would've changed if he did.