Hi Mark -- I just installed Wordfence, activated it on a local, multisite install and immediately got the following error:
Wordfence generated an error on activation. Please report this on our support forum. The output we received during activation was:
<b>Notice</b>: get_bloginfo was called with an argument that is deprecated since version 2.2! The
siteurl option is deprecated for the family of
bloginfo() functions. Use the
url option instead. in <b>/Applications/MAMP/htdocs/wp34/wp-includes/functions.php</b> on line <b>2789</b>
<b>Notice</b>: get_bloginfo was called w...[output truncated]
A quick multi-file search of the Wordfence directory shows there's a call to get_bloginfo('siteurl') in wfAPI.php, like 158.