How do certain programs run without permission?

Question

I'm just wondering how people can write programs that as soon as they're downloaded, they run, like viruses. What language is used? what kind of commands?

I'm not looking to write a virus, just trying to get a good understanding so I can explain to friends when I help them with their PCs

Answer 1

The most ironic cause is the file is scanned by a virus scanner. During the scan, the AV program inadvertently executes the code buried within the malicious software. This type of viral program is rare though.

Most often the code is executed by a flaw in another piece of software, like IM programs or email clients. The malicious software enters through a 'hole' in the back and goes from there.

Answer 2

Here's the problem

when you were assigned a password and log on to your new pc you gave yourself administrator rights
When you dfownload a virus the virus has your rights
the way to fix this is NEVER to use Root or Admin rights always sign on as a regular user NOT a super user

Answer 3

well computer virus are mainly wrote in c++, visual basic, and comm, you can also read http://en.wikipedia.org/wiki/Computer_virus