Mac Update has caused no use of mouse!

I did a Mac (security?) update this morning, I couldn't even tell you what one it was but it's obviously new this week. Since I restarted my computer as it prompted me to, I've been unable to use my mouse! It's as if someone is pressing Ctrl or Cmd or something permanently, except they're not, I've checked my keyboards, I have 2 mouses and they do they same thing as well. I don't understand what's happened and I can't click anywhere because of this problem & am really unsure what I'm meant to do next! Any tips please?
Thom

First, can you tell us which Mac model you are using and also which version of OSX? There was a security update for 10.5 Leopard also the same day the 10.6.5 update came out.

Also does the pointer move when you move the mouse/trackpad? Just clicking not working or nothing working?

I believe I have leopard - not snow leopard (that's the last one right? and the new one is going to be Lion? I got it at the end of 2007).

The mouse moves yes, but I can't click or anything due to this. I can use the keyboard fine. It's as if someone's pressing ctrl or cmd or alt (not sure which) all the time except they're not, that's the effect it's having on the mouse...

Try going to  > System Preferences > Mouse

make sure the primary button is the left one

I would but I can't click! Is there a keyboard shortcut?

When you get to the mouse preferences, use the tab key. You will see each button and arrow highlight very subtly. Tab to the mouse button radio buttons and use the arrow keys to change the option.

I can't even get to system preferences due to not being able to click

Just a thought - what happens when you use the right mouse button?

Do you have a portable with a trackpad - does that work?

if you can get to the finder press  -shift-G

in the Go To dialogue paste in this command

/System/Library/PreferencePanes/

The folder containing all of the preference panes should open up. Use the arrow keys to select Mouse.prefPane

Press O (Ohh not zero) to open the mouse prefs using the keyboard only

Hi - thanks ever so much for your help guys. Peculiarly, everything is working fine now, after I left it on 'sleep' for a few hours whilst out, really very bizarre.