Computer history problem

[Elvalight]

Ok, so this weird thing happened earlier. So I was doing homework, and my mom called my sister downstairs. She sounded angry, so I followed.
She said that someone had searched for porn on youtube. Now, I don't look at porn( I'm asexual; and if I did, I wound't do it on youtube) and my sister, who tells me everything, said that she didn't either.
This wouldn't even be such a problem, but she's really conservative.
There's also my dad, but he's also really conservative, so he couldn't have done it. She somehow found it while searching for something in her computer's history, which doesn't make any sense.
From what I've researched, you shouldn't be able to find the history for a computer through another one, unless you called up the internet service providers.
I mean, yeah, I see R rated things every now and again, so if she could see my history, she would have said somehow a long time ago. So that means that someone searched porn on her account.
It just doesn't make any sense to me. Is there any way an account like hers could be hacked or something?
Now I'm super scared she'll install something to track everything me and my sister do online or call the internet service provider to see our history. Help?!

[sqishy]

I know relatively little (least that I know of); have you tried using incognito browsers? Hope my tiny suggestion helps.
You could use a randomised-IP browser like Tor too. It does not have as many capabilities as like Firefox or 'normal' browsers, but it does not store any history or anything whatsoever related.

[lancezer]

it's not been logged out on a computer go to gmail and in bottom corner details and will show computers connected and click log out all other sessions done your welcome

and yeah in private browser or incognito tab under menu on chrome or Firefox etc same place as new tabs
in the above menu in browsers or on phone in settings

-merged double post. -Emerald Dream.

[Typhlosion]

Icognito mode does not leave tracks, truly...

As for how it got there, assuming it was none of your family, maybe a colleague of yours searched for 'porn' on one of your phones when you weren't looking. Youtube's search history is synchronized over devices. The idea of finding another computer's history is completely absurd, and is also the idea that anyone would hack a family computer to... search for porn. The ISP also has nothing to do with this; while they do keep a record of your browsing requests, their history record has nothing to do with the computer's local history record. Regardless of going icognito or not, the ISP will have it logged.

[Elvalight]

Going incognito does nothing to keep history from being recorded by an ISP. So, technically, going incognito does nothing for me except maybe keep my cache to a minimum, keeping it from running slowly, and I use it already all the time( thanks for the tip, though.)
More than anything I'm just worried that my dad was searching it. Awkward much? o-0
As I said, a person hacking it, while a possibility, would probably not search porn.
I still have no idea how it happened. Nothing like this has happened before( to the most of my knowledge) and nothing has happened since.
Still also a possibility that my parents will contact our ISP or set up a internet nanny or something.
It took my long enough just to get the internet free of restrictions at my house, so you can imagine how this is for me.
If there are any other possibilities that you can think of, please share.
I mean, I know this isn't a computer-specific site, but this was all I could think of :/

[qaisr]

Please turn off Google search syncing, it is possible to even view how frequently you visit searched sites, even in incognito, or private browsing, so as long as your Google account is signed in. Those simply destroy locally stored data. Delete all of your web activity history and go here (https://www.google.com/settings/accounthistory/search) to pause your history completely. You may also simply log out of your Google account and log back in when you need to privately browse. I no longer use Google and only use ixquick infrequently with ublock, umatrix, https everywhere, privacy badger, a few tampermonkey scripts, tracking protection, and don't track signals on my firefox. Typically I use lynx to browse anyway.

ISP logging varies from company to company, typically it is a 6 month data retention policy. Your ISP also does not disclose data unless ordered under court-of-law. See if someone else's account is signed in on her device or if someone else used her device.

Tor does not randomize IPs, there are actually a very finite number of exit nodes. However, it is secure to your ISP due to encrypted "onion routing", as is a secure VPN, as is a secure proxy.

[randomuser123]

In short - yes it is pretty damn easy to read history. The cynic in me says that your sister is lying in case you let on something to your parents. Without formatting the hard drive you can read someone's history...even in incognito or private mode. It isn't hard...I can do it if I so desire.