[Громовник]

If you are running a default Ubuntu install, the root account is disabled, so no worries there. The user is the biggest security problem, make sure you set a strong password, and practice safe computing.

In general, Windows malware doesn't work on Linux, not even on Wine. These things invariably exploits a very specific hole in a Windows system, which doesn't exist in Linux.

That being said, it is possible to exploit a badly configured Linux system. If you use a kewl 4 letter password and installed VNC, FTP, Apache and other servers, then your system can possibly be hacked.

If you use a default Ubuntu installation and you set a 12 character password, then not.

So it is completely up to you, how hackable your system is.