My experience with cleaning up this type of problem is that when you get nudity-containing ads and are not on an adult themed website, the most common cause of this is a trojan horse or virus program. If so, ad blocking software may be ineffective at solving the problem. Further, these trojan and virus programs can be doing other bad things, such as using your computer to send spam, etc.
If you recently installed any browser helpers, toolbars, etc., before this problem started the newly installed "helper" is probably causing these ads. If so, first uninstall the helper software, toolbar, etc.
Then run a virus scan with software that also detects trojan programs, malicious toolbars, etc. Download and run these 3 programs:Spybot Search & DestroyAdAwareCCleaner
When you first run these programs, they will update with the latest virus definitions.
If this problem persists after running these programs, restart your computer in SAFE MODE and run the programs again. The reason for this is many virus programs launch at startup, and also launch a hidden program that checks to see if the virus program has been removed, and if so the hidden program reinstalls the virus! By starting in safe mode you keep the virus AND the helper program from starting, and the software can remove them both. But you need to have the latest virus definitions, which is why you run these programs in regular mode (connected to the internet) first.