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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 (firstname.lastname@example.org; 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.
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.
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?