Hello. Just bought a brand new macbook pro retina 13.used for 3-4 months only.

When i used imovie to edit videos, there was some serious fan noise coming out of the device. This worried me a bit. Is this normal?

Im a serious multitasker so i run many apps at one time. Suddenly it forces shut and restarted. Wrote something like the first post on this thread. I read the first aid and did the disk utility, it says the disk is fine. I haven't bought any antivirus yet and i download a lot of pdf n music from online, could this be the cause?

And wht type of antivirus suitable to buy thts not gonna burn my purse?

Thank you so so much!