Jody brings up an interesting point and it is a widespread curse;
it seems to infect PCs more than Apple computers.
Having some long time friends in the business who are employed by
both firms, I know this for a fact: both Twitter and Facebook do
insert hidden cookies into personal computers, iPads and some other
things that permit web searching. They do look for key words that
you might frequently use and capture your address. Then they sell it
to advertisers who pollute your device with unwanted advertisements.
The only cure is to know and use a really skilled computer programmer,
maybe the 15-year-old down the block, and have your computer swept and
cleaned out every six months or so. These cookies can be found and
removed. It works, too.