When I got a new computer a few months ago, I didn’t add any protection. I barely had time to get my programs reloaded for things like my camera. Well, I paid later for not taking the time because I ended up with some annoying stuff on my computer.
Here are two links for free, effective, and quick protection from ads and viruses. Of course there are paid upgrades available from both. This fixed my problems right away and gave me time to look into other options for computer protection.
Ad-Aware for ads (it got rid of excessive and annoying pop-ups) and AVG for virus protection.