This is must reading if you spend any time online.
… while reading the New York Times online, I was confronted with an attempted security attack, apparently delivered through an advertisement. A window popped up, mimicking an antivirus scanner. After “scanning” my computer, it reported finding viruses and invited me to download a free antivirus scanner. The displays implied, without quite saying so, that the messages came from my antivirus vendor and that the download would come from there too. Knowing how these things work, I recognized it right away as an attack, probably carried by an ad. So I didn’t click on anything, and I’m fairly certain my computer wasn’t infected …
Source: Freedom To Tinker blog.
Like the man so tiresomely said in Hill Street Blues, “Be careful out there.”