Well, someone, from somewhere in Egypt (according to Google's assessment of the IP location) got into my GMail account. Thanks for that, I didnt have anything else planned for today so have spent hours changing passwords and contacting people to apologise for sending them links to Canadian Pharmacy websites.
Just in case you have any similar unfortunate experience here some basic instructions/recommendations from http://www.google.com/support/forum/p/gmail/thread?tid=44ef855684a3f46e&hl=en
If your account has been compromised/hacked/stolen you will need to check and fix at least all of the following settings.
But first you need to check the bottom of the Inbox and make sure your account is not open at any other locations. If it shows additional locations, open the Details window and "Sign out all other sessions".
Account Security:
Settings -> Accounts and Import -> Google Account Settings -> Change Password [pick a new secure password]
Settings -> Accounts and Import -> Google Account Settings -> Change Password Recovery Options [verify secret question, SMS and recovery e-mail address]
Potential Spam:
Settings -> General -> Signature [make sure nothing as been added]
Settings -> General -> Vacation Responder [make sure it's disabled and empty]
E-mail Theft
Settings -> Accounts and Import -> Send Mail As [make sure it is using your correct e-mail address]
Settings -> Filters [no filters that forward or delete e-mail]
Settings -> Forwarding and POP/IMAP -> Forwarding [disabled or correct address]
Settings -> Forwarding and POP/IMAP -> POP Download [disabled]
Settings -> Forwarding and POP/IMAP -> IMAP Access [disabled]
Additional Information
Keeping account secure: https://mail.google.com/support/bin/answer.py?hl=en&answer=46526
Protecting your account: https://mail.google.com/support/bin/answer.py?hl=en&answer=29407
More account security info: http://www.google.com/help/security/
If your account is compromised: http://mail.google.com/support/bin/answer.py?hl=en&answer=50270
Someone using your address: http://mail.google.com/support/bin/answer.py?hl=en&answer=50200
Google Employee comments: http://www.google.com/support/forum/p/gmail/thread?tid=560d53dee40be5e6&hl=en&start=70