What is a user agent?

[itrainu]

I wasn't all that concerned about user agents until this Aaron Carter thing showed up in my logs and I saw a post here about it.

Can someone explain this to me?

Thanks ;-)

itrainu

[Pushycat]

User agents are how various pieces of Internet software like browsers identify themselves to a website. It's just some text that might, in my case, tell a website I'm running IE6 SP1 on Win2000. Or it might be Google telling me she's back for another dance. Or it might be some nefarious website stripper that's there to bring my server to its knees.

[korkus2000]

A user agent is the program that downloads your web page. What you see in your logs is how it identify's itself. The Aaron Carter agent was from a user who changed how their program identified itself.

User agent for Internet Explorer 4.01 on a windows 98 operating system:
Mozilla/4.0 (compatible; MSIE 4.01; Windows 98)

User agent ZyBorg from looksmart for the wisenut search engine:
Mozilla/4.0 compatible ZyBorg/1.0 ([e-mail]; http*//www.WISEnutbot.com)

User Agent for the link checking program Xenu:
Xenu Link Sleuth 1.2c

User agents let you know what programs are looking at your site. Most of us use it to track search engine spiders. Used with the user agents IP address it can let you narrow down who this user is.

[Jack_Straw]

Everything Pushycat and korkus say.

And:

The user agent field in your logs is from the value of the HTTP_USER_AGENT field found in your visitors HTTP request header. This value is assigned by the software your visitor runs. This value is very easily and frequently spoofed. Even mildly sophisticated visitors can set the user agent field to anything they want.

Most agents identify themselves clearly and honestly. But, there are a lot of bad agents that mis-identify themselves for different purposes. For example, software robots that crawl the web looking for email addresses to add to their spam lists sometimes identify themselves as a browser because so many webmasters block them from thier site.

[itrainu]

Thanks for the responses!

Quick question - I have not found the need to block anyone/anything yet, but should this concern come up in the future - how is this accomplished? Possibly through the control panel provided by my ISP, which is where I access my weblogs, create custom error pages, etc?

Thanks,

Perennial2

[korkus2000]

Which operating system does your server have? Unix/Linux/Windows