Whenever I use my PC "security warning", saying that PC is infected with "trojan.W32.

This started when I started visiting adult sites. Also whenever, I restart PC, desktop shortcuts "Spyware%26Malware Protection", "Privacy Protector" %26 "Error Cleaner" appear automatically. Moreover, IE also initiates automatically taking me to URL "Ihttp://ucleaner.com/main.php?wmid=6010... Also this URL becomes my home page automatically. I have installed latest version Avast anti-virus. How do I get rid of this problem.

Whenever I use my PC "security warning", saying that PC is infected with "trojan.W32.looksky" appearsabtuvurys 2005

You computer has a serious Vundo infection causing this.

The specialized removal tool called RogueRemover is said to remove it:

http://www.malwarebytes.org/database.php

Use the free version. There is absolutely no reason to use the paid, "Pro" version when you want to remove only.

Good luck.

Whenever I use my PC "security warning", saying that PC is infected with "trojan.W32.looksky" appearsantivirus programs

i had the same problem awhile back. heres what i did: i downloaded "ccleaner". you can go to their wesite and download the free version, it cleaned out all that garbage, now my pc works fine. when you get "ccleaner" make sure you check all the boxes and then run the "cleaner", it should put you back where you want to be and watch out for those adult sites, they're full of malware and all kinds of other stuff. hope this helps, good luck.
Download the programs linked below. Install them. Update them. Scan your pc with them.