Browser statistics are as easy to obtain as any other data. But, keep in mind, during a hack attempt browser information can be masked, hidden or spoofed in the hacker's script. But in general your browser info is fairly accurate.

You can modify the script above to include the following lines to write to the text file:

$s_user= 'HTTP_USER_AGENT: ' . $_SERVER['HTTP_USER_AGENT'] . "\n\n";
fwrite($fp, $s_user);

The $_SERVER['HTTP_USER_AGENT'] will glean the specifics on the visitor's browser.

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I use Country IP Blocks as added security for my networks and servers.