Adware Medic didn't solve all of the problems so I will try the other recommendations. As for preventative recommendations, I've been using Macs since 1984, probably before some of you were even born. I know how to be safe but might be getting a little careless in my old age.
A throw down! Wrong thing, CyberGranny! I built my first computer in the 1970's from components. The first "store bought" was a TRS-80 Model I in 1979, which I then modded to add upper and lower case letters, a board to let it boot CP/M and an expansion interface to crank the memory from 16K to 64K (48K in CP/M). I'm relatively new to Macs, just 8 years, but I've been around the block a couple of times. I've run DOS, PC-DOS, CP/M, Fedora, RedHat, SUSE, Ubuntu, and a couple of other variants of Unix/Linux, now OS X. I was in networking with BitNet (before the Internet), ran a bulletin board (8 telephone lines in--the police thought I was a bookie, seriously!). Programmed in Assembler, Fortran, COBOL, Basic, Pascal and Ada. And I'm not the oldest here, I'm only 69.