Questions[viruses](ubuntu)

I have a fresh installation of Ubuntu 12.04, I have been running it for about a week. Suddenly today I noticed my computer freezes every 5 seconds. I restarted the computer and I still get this. I believe it is a process called watchdog/0 that is using all the resources. See the attached pictures.

How can I stop this? I can barely use my computer like this.

UPDATE

Well I just did a cold reboot, (shutdown, unplug, and plug back in, and turn on) and it seems to have fixed it. After looking at the man page for watchdog, it seems that this process may stay on during a restart? so it is more like a soft restart? Why that happens I don't know.

Possible Duplicate:
Do I need to have antivirus software installed on a Linux distro?

I'm using ubuntu right now and I think it's really good. Really. But I'm wondering about viruses. I come from a mac background (I have never got a virus) and I'm wondering how ubuntu does the same. It has "millions of users" so I'm wondering why someone didn't make one yet. Or does it have built-in protection?

Switched my sister to Ubuntu because I got tired of re-installing the other OS every 6 months. Now she managed to get some malware in her Firefox on Ubuntu. Without access to the computer (or when I get it next week), where should I look, what questions can I ask, what could I tell a computer novice to try over the phone?

Symptoms:
While surfing some recipe site she had an ad-window pop up with no window controls. She rebooted the computer and when she re-started Firefox it came back, full screen, no controls, on top.

I told her to just use -F2 and xkill to get rid of it, which it did but stopped Firefox completely. On re-start it was back, I told her to hit F11 which did take it back to a large screen, but not full-screen, so she could see that there was a normal browser window running underneath. She topped the normal window but the only other thing I had time to check was plug-ins, which there wasn't anything that sounded suspicious. I'm looking for ideas of what to try over the phone, or where to start next week.

I'm comfortable with the command line, and using about:config if that makes any difference in the answer.

As Linux continues to grow and develop, and the more we use Linux, the greater the threat from viruses.

We also know that a virus/threat in Linux (if any) would have difficulty running or spreading when it is running as a normal user, but it is a different story if the virus/threat is running as the root user.

An example of this danger would be if a virus is tucked inside a PPA (intentionally or unintentionally) or if an application has an intentionally planted backdoor (e.g., pidgin could secretly send passwords to a particular address).

If we add software from a Launchpad PPA, is there any guarantee that software is from free viruses/backdoor threats?

I've got a file said to contain information I was looking for. Unfortunately it is an executable instead of DOC (as it was meant to be) and the site I've download it from looks suspicious for me. If I was not using Linux, I'd run it on a VM or a separate PC. But running Linux, do I need to worry, or can I just run it with Wine? Can Wine system be infected?