4
What kind of block is this?
If it belongs to a module, it has a "show-function" whose location you can determine by looking at the module's xoops_version.php file.
Example (from modules/system/xoops_version.php):
$modversion['blocks'][1]['file'] = "system_blocks.php";
$modversion['blocks'][1]['name'] = _MI_SYSTEM_BNAME2;
$modversion['blocks'][1]['description'] = "Shows user block";
$modversion['blocks'][1]['show_func'] = "b_system_user_show";
$modversion['blocks'][1]['template'] = 'system_block_user.html';
That block's show-function is named b_system_user_show and is in the file system_blocks.php (in the directory modules/system/blocks, since this example uses the system module).
If it's a custom block, it doesn't really have its own show function. You could place PHP code within the block to do the check, but I don't think there's any way of completely suppressing the block with that method; you could suppress the content of the block, but the title would still display.
For the detection code, you could examine the variable $_SERVER['HTTP_USER_AGENT'] using strpos() or preg_match().
