A Simple Way to detect spambots
This is an old trick but worth being mentioned again:
<textarea id=”spammed” name=”spammed” rows=”3″ cols=”4″></textarea>
now hide this textarea using javascript / css, by setting the display to none. Now when the form is submitted if you find any text here you can safely assume its a spambot. 
Microsoft Anti-Cross Site Scripting Library V1.5
This download link contains the redistributable files for the Microsoft Application Security Anti-Cross Site Scripting Library. The Anti-Cross Site Scripting Library can be used to provide a high degree of protection to Web-based applications against Cross-Site Scripting (XSS) attacks.
Coolite - ExtJS Controls For ASP.Net
A suite of professional ASP.NET Web Controls built on the Ext JavaScript Framework.
How to change some attribute on a certain type of elements in an entire page
Using javascript, you can do this. Some changes are required to suit your code. You have to replace
YOUR-ELEMENTS-TAGNAME with your HTML Elements Tag Name.
YOUR-ATTRIBUTE-NAME with the attribute name that you want to change
and YOUR-ATTRIBUTE-VALUE with the value of the attribute.
function changeAttribute(){
var elements = getElementsByTagName('YOUR-ELEMENTS-TAGNAME');
for(var i = 0; i < elementss.length; ++i){
links[i].setAttribute('YOUR-ATTRIBUTE-NAME','YOUR-ATTRIBUTE-VALUE');
}
}
Now call this function in body - onload.
How to change some attribute on a certain type of elements in an entire page
