This page ~~Snip~~ pops up if I leave my computer unattended for just a few minutes. It seems it is related to my homepage being hijacked: if I open a new tab in Chrome the URL is blank, but the page shows icons for Facebook, Twitter, and other common applications; it is clearly not my usual Google home page. None of this is by choice.
I understand this may be a malware attack, but I don't know what to do about it. Please, help me make it go away.