I'm interested in know more about this as well. I've always thought that the danger of others knowing your IP address is that it allows them to try to connect to your pc while you're online.

They can certainly find out the ISP's details and approximate geographical location.

Usually however they won't be able to get your private details such as your name, address etc.
There are some exceptions
1) Auto-complete vulnerabilities in various browser e.g. The Safari one [webmasterworld.com...] although I have seen others mentioned as well as having similar issues.
2) If they can legally request your details from your ISP.

Unless they somehow compromise your machine, they won't know what websites you are working on.

dertyfern, I hope you are running some sort of firewall client that would stop people trying to connect to your computer.

Dijkgraaf, just running whatever's installed with either Windows Vista and Avast antivirus software. Is that sufficient?

Some people might find it debatable if Windows Firewall is sufficient, but yes, that should stop stuff.

Thanks

My last ISP had things set up so that a reverse lookup actually assigned my name to the IP address. Yes, you could get my real name from my IP address. Pretty sure my new ISP doesn't do that.

trying doing a traceroute on some ip addresses and see what it shows you.

They can certainly find out the ISP's details and approximate geographical location.

Usually however they won't be able to get your private details such as your name, address etc.
There are some exceptions
1) Auto-complete vulnerabilities in various browser e.g. The Safari one [webmasterworld.com...] although I have seen others mentioned as well as having similar issues.
2) If they can legally request your details from your ISP.

Regarding Number 2, do you think this is something a website would do (a small site or a large one with forums possibly) to have a better idea of who is visiting them or is this something that websites don't really do?

Also, if a website you visited wants to request your information from your ISP, does the ISP have to notify you first that there is someone asking for your information or can the ISP give the information to the website requesting it without making you aware of it?

Regarding Number 2, do you think this is something a website would do (a small site or a large one with forums possibly) to have a better idea of who is visiting them or is this something that websites don't really do?

This isn't a matter of a simple request from any Tom, Dick or Harry. At least not in the States. This would be by a legal subpoena in a criminal or civil case.

I wouldn't think this is something a website would normally do; and as jimbeetle said your ISP is unlikely to release this information unless they were legally obliged to do so.
As to whether the ISP would have to inform you, it would depend on the laws in force in the jurisdiction which the ISP operates.

Normally from the IP they can just get your host provider and geographical location and to get more specific information would require asking the host provider directly. But there are a number of cases where an IP can give uniquely identifying information:

- if you post on a forum that displays the IP address of the poster they can attach you to any information that you have posted (name, pseudonym, email address, etc). There are not many of these but there are some.

- if a website/forum is incorrectly configured or poorly designed in such a way that admin accessible only information can be spidered by a search engine such as goole, then googling the ip could display that information. I've only found this once, but it is a serious breach of privacy.

- More worrisome is the "HELO" element of the email header. Email clients like Microsoft Outlook send the name of the host computer sending the mail (your computer). So if you have named the computer with your name (John Doe is worse than John's Laptop) then that will go out in the header of every email you send. Cell phone providers have in the past sent the mobile phone number as the HELO.

- Most email programs also send your IP in the header of emails you send, so in that way it is easy to connect a person and email to an IP address. Once somebody has either of these, if they are a serious hacker they can monitor a great deal of your online activities (if you have a static IP).

So if somebody is interested in connecting you to an IP, the first thing they would usually do is send you an email that you will reply to.