Now im getting a couple of disposable email accounts in users table, how can I avoid this nasty situation?
You might need this plugin: http://wordpress.org/extend/plugins/no-disposable-email/
Thought I would add to this answer as none was specified and it took me a while to find a solution.
What I am using is the blacklist method where you specify a list to block. It works well as users just give up after trying the biggest disposable email providers.
The code can be found here: How to Block Disposable Email Addresses: PHP Code
It works by letting you create an array of domains you which to block. You then provide an email address as a variable and this gets split to get the domain. This is compared to the list and as you can see on the website you can do whatever you like if a disposable email is detected.
please also have a look at http://wordpress.org/extend/plugins/block-disposable-email-addresses/ which is a plugin for wordpress that uses http://www.block-disposable-email.com/