How can I find and replace all URL's using regular expressions in PHP?

[VOearl]

My URL's might not be well formatted, so it could be \[code\]http://www.google.com/\[/code\] or \[code\]www.google.com\[/code\] or \[code\]google.com\[/code\] and it'll be in a block of text like:\[code\]This is google.com and it rocks!\[/code\]I need to find the website and replace it with \[code\][*********]\[/code\]Any ideas?