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140 votes
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My ISP uses deep packet inspection; what can they observe?

Deep Packet Inspection, also known as complete packet inspection, simply means they are analyzing all of your traffic as opposed to just grabbing connection information such as what IP's you are ...
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139 votes

If I delete my router's history can my ISP still provide it to my parents?

If I delete my router's history, is it still visible and can my ISP still provide it to my parents? Or is it deleted from existence? Your ISP's record of your network usage isn't in any way affected ...
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99 votes
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How can ISPs handle DDoS attacks?

There are a number of strategies, each having their own costs and benefits. Here are a few (there are more, and variations): blackholing By blackholing traffic, you discard all traffic towards the ...
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  • 6,788
87 votes

If I'm currently on a website and disable my VPN, is my ISP or the web server immediately aware of the change or does a page refresh have to occur?

In the early days of the web, webpages were mostly static and there would be no communication between your computer and the web server unless you were actively loading a page. Today, that is no longer ...
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  • 10.2k
65 votes

My ISP uses deep packet inspection; what can they observe?

Trey Blalock's answer describes percisely what deep packet inspection (DPI) is. But I'd like to add three things to hopefully answer your specific questions: There is a technique of DPI that does ...
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  • 2,284
62 votes

Does your ISP know what type of phone/computer you're using?

Depends on the device and if you have taken any steps to hide it. Most devices by default put a lot of identifying information in the User-Agent header on outgoing HTTP/S requests. For HTTP requests ...
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  • 10.9k
57 votes
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Can ISPs replace a website's HTML/JavaScript/HTTP headers with something else?

Your ISP is per definition a MITM (man-in-the-middle) and therefore can serve you any content it desires. You mentioned HTTPS and this is of course a game changer. Yes, the ISP can server any ...
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  • 7,214
52 votes

Received email from ISP saying one of my devices has malware

Can an ISP really detect this? The ISP can see all data your systems exchange with the internet (but not the plain text from encrypted data). Based on this he can detect botnets which often show ...
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42 votes

Does your ISP know what type of phone/computer you're using?

I worked for an ISP and yes we do. We know many things about your systems in the house. A lot of them we learn from the router that we provide you, from vendor Mac addresses, from various headers ...
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41 votes

My ISP uses deep packet inspection; what can they observe?

As stated by Trey, DPI can see the entire content of your network traffic. All of it. If it is plain text, then they see everything that you do. To add on to Miao's answer: Things DPI can see, ...
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  • 1,141
38 votes

If I delete my router's history can my ISP still provide it to my parents?

Routers usually do not store history and ISPs, while they may record such things on internal logs, do not give them out to anyone without a court order. You do not need to worry about your parents ...
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  • 64.1k
33 votes

What parties have access to the *full* requested URL of a website accessed via the HTTPS protocol?

Only the TLS endpoints1 can read the the full URL because HTTPS provides end-to-end encryption. HTTPS wraps the full HTTP protocol, including the request line, request/response body and all the ...
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  • 43.8k
30 votes

Can two locations in the same city at the same time have the same IP adress?

Details here depend on your specific ISP setup, but it might well be that multiple customers share the same public IP address. This is called NAT or in case of ISP CG-NAT (carrier grade NAT). It is ...
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22 votes

Can my ISP see which VPN protocol I am using?

Yes, probably. Most VPN protocols are not designed to hide the fact that they're VPN protocols, nor what kind of protocol they are. See for instance this paper which details fingerprinting OpenVPN. If ...
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  • 12.6k
21 votes
Accepted

What does my ISP see if I change my DNS server?

So, I think, that when I type certain URL in my browser (for example https://google.com) I send request through ISP to ISP DNS and my provider gets response (ip of google.com) and goes by this IP and ...
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19 votes

Received email from ISP saying one of my devices has malware

This looks like a legitimate email. Someone detected that a computer with an Indian IP address was part of a botnet. This was shared with your National CERT (CERT-In). In turn, as they didn't know ...
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  • 17.3k
18 votes

If I'm currently on a website and disable my VPN, is my ISP or the web server immediately aware of the change or does a page refresh have to occur?

It depends on the site. Does the website have any javascript function sending data back from time to time? Open the Developer Tools on your browser, go to the Network tab and watch. If there's ...
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  • 50.5k
16 votes
Accepted

Does Tor help us to prevent ISP tracking?

You cannot hide how much data you are sending and when you are online. But, Tor encrypts data and sends it through proxies before it reaches the target server, so that hides the contents of the ...
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  • 31.9k
12 votes

If I delete my router's history can my ISP still provide it to my parents?

ISPs can absolutely log traffic upstream from your router. The easiest way for an ISP to inspect what users are doing is by inspecting logged dns queries. People can get around this by using non ISP ...
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  • 441
11 votes

Received email from ISP saying one of my devices has malware

The email address from which you have received the mail seems genuine. The body of the mail also adds to the genuineness. However, senders email addresses can be spoofed by using open mail relays. As ...
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  • 186
10 votes
Accepted

How DNS is leaked?

I think you are a bit confused about what DNS leakage is and isn't. The problem with DNS leakage isn't that the website knows what DNS server you are using. The issue is that the DNS server knows ...
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  • 301
10 votes

Can two locations in the same city at the same time have the same IP adress?

Contrary to what some moderators in some communities believe, IP addresses are not a reliable personal identifier. Some ISPs use carrier-grade NAT, which means that a large number of users share the ...
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  • 48.8k
9 votes

My ISP shows my WiFi password on their public site in plain text. Should I be worried?

What surprises me here is not the fact that the passwords are displayed in plaintext, but that your ISP keeps a copy of your wifi password at all. This is not something they need to do in order to ...
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  • 64.2k
9 votes
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how is my ISP able to inject into this webpage?

Your screenshot shows an HTTP ("Not Secure") page, not HTTPS. Your ISP essentially pulled an "SSL Stripping" attack on you; they blocked you from getting the redirect, fetched the ...
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  • 39.6k
8 votes

Does your ISP know what type of phone/computer you're using?

Short answer: YES How? MAC ADDRESS & TCP/IP stack profiling ISP provided routers have access to your phones MAC address which is unique to your device and thus the manufacture of your device ....
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8 votes
Accepted

How does DNS over TLS prevent your ISP from seeing the websites you visit?

It doesn't. DNS over TLS is not designed to keep your privacy from ISP. Like HTTP, DNS is vulnerable to MITM. DNS over TLS provides the same level of security as HTTPS. As DNS over TLS is encrypted, ...
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  • 6,061
7 votes
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Do major ISPs still ignore IP spoofing?

I first saw the original referenced question and answered there, but I'll copy/paste my answer here since and add some more details to your additional questions: ISP's should implement anti-spoofing. ...
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  • 6,788
7 votes

If I delete my router's history can my ISP still provide it to my parents?

Your parents will not normally have the authority to retrieve data from the ISP. An ISP does not offer this type of information on request. You need some type of government warrant before they're ...
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  • 339
7 votes

Can ISPs replace a website's HTML/JavaScript/HTTP headers with something else?

Yes, they can. The important part is HTTP is still the default protocol in 2020. Most sites use HTTPS today, but it works by first doing an insecure request which will redirect to HTTPS. This means, ...
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6 votes
Accepted

Can restarting a router result in its software being updated?

Short answer: It erases the volatile memory, which is where the plug-ins are stored that you're referring to. This was what was doing the heavy-lifting of the malware. To fully get rid of malware, ...
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