I was working on the Internet yesterday and suddenly a very ugly picture appeared of a naked woman I was shocked. How can this happen?I deleted it but without results; it formed an icon. I spent all last night in erasing that ugly picture. I was wondering about my brothers who work on the Net; how can I protect them from these pictures sent by unknownPersons I am very worried.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Though the question needs more details, two points are to be focused on:
1) How to avoid bad pictures produced by downloading certain programs … as understood from the question.
2) How to protect the PC from such pictures.
Answer to point (1):
You said that you had found bad pictures having an icon. This proves that they are not merely pictures. So, although you deleted them, they reappeared. You deleted the shortcut of the program but the program itself was still there in your PC. So you have to delete it.
Ways of Deleting Programs (in brief):
A) By "Add/Remove program".
Do the following:
Start >> settings >> control panel >> Add/Remove programs
You will see a page showing the programs downloaded. Double click the unwanted ones and then delete them.
B) By "Uninstall".
Some programs are downloaded along with accompanying programs that give you the option of removing undesired programs.
So you have to search the program menu for the program you want to delete, and if you find its accompanying program, then open it and delete it.
Start>>programs >> [xxx program] >> uninstall
C) By Ordinary Deletion:
(Follow this method only after the previous two ways fail to work, for it may leave some files undeleted or may cause some minor problems).
(1) Right click on the icon.
(2) Choose "Properties"
(3) Choose "Find Target".
Here you will see a new window showing the original location of the program along with its attachments - delete them all.
(NB: There are other ways and programs for deletion).
Deletion of Temporary Pictures while Browsing the Internet:
- Open Explorer.
- From the upper Menu. Choose Tools >> Internet Options >> Delete Files >> This will delete all pictures and downloads.
- "Clear History" => to delete the titles entered through the explorer.
Answer to Point 2:
- Regarding protecting the PC, it is impossible unless the user fears Allah Almighty in his privacy.
- There are some programs that prevent most of the pornographic sites, but do not prevent e-mailed pictures or pictures sent through chatting programs.
 

Allah Knows best.