How does your email account get hijacked?

[SexyGreyFox]

Many a time I've emailed friends to tell them to change their hotmail, gmail or other email account password because I've had emails from them with viagra or other such links.
Does changing the password make any difference?
How is the email address hijacked but more importantly, how do they find out your contacts?
How can you stop it?

I've got one woman in the office who is very upset that she has supposedly sent an email at 2am to around 25 contacts with a rather saucy link in it (2replied asking what was going on).

Any info appreciated

 

[SexyGreyFox]

Brute force on the password or security question or password intercepted via keylogger.

Use strong passwords and security questions which cannot be guessed easily or answered with easy research. Run decent anti virus and anti malware. Don't use IE

Does this mean that the person doing it can actually get access and read all the emails of my colleague?
If that is the case why don't they go into the settings and change the password to really upset my colleague (I've never heard of this happening)?

 

[SexyGreyFox]

Thanks everybody.