Applications keep closing unexpectedly, virus?

Question

Recently, while using my computer, applications started closing unexpectedly. Activity Monitor shows that RAM and CPU are at normal levels. Also, the computer regularly freezes, and acts oddly. I did a reset - turn off computer, hold Shift, Control, Option and Power Button at the same time, release, then power on by pressing Power Button. It helped a bit, but applications still close regularly... By the way, I get the error message, prompting you to send an error report to apple when the apps close. Before the reset, I tried several times to do a scan with iAntiVirus (app store No.1 free app, made by Norton), but each time, it either froze up LOADS or the computer restarted... Suspicious. I understand that macs can get viruses, but unless this is a delayed action virus, I don't know how that is possible... The only thing I downloaded recently was a plugin for a game: it had many positive comments, so that can't be a virus... What do I do?
NOTE: I am writing this on a seperate computer. For obvious reasons.

Answer 1

Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad. Click Utilities, then Console in the icon grid.
Step 1
Make sure the title of the Console window is All Messages. If it isn't, select All Messages from the SYSTEM LOG QUERIES menu on the left.
Enter the name of the crashed application (Safari) or process in the Filter text field. Post the messages from the time of the last crash, if any — the text, please, not a screenshot. 
When posting a log extract, be selective. In most cases, a few dozen lines are more than enough.
Please do not indiscriminately dump thousands of lines from the log into a message.
Important: Some private information, such as your name, may appear in the log. Edit it out by search-and-replace in a text editor before posting.
Step 2
Still in the Console window, look under User Diagnostic Reports for crash reports related to the process. The report name starts with the name of the crashed process, and ends with ".crash". Select the most recent report and post the entire contents — again, the text, not a screenshot. In the interest of privacy, I suggest that, before posting, you edit out the “Anonymous UUID,” a long string of letters, numbers, and dashes in the header of the report, if it’s present (it may not be.) Please don’t post shutdownStall, spin, or hang logs — they're very long and not helpful.