No one likes adware in the first place, but a particular piece of adware, Superfish, is being called out now as particularly bad by security researchers. It's been preloaded on many Lenovo computers too. But there's an easy way to see if you're vulnerable.
In a nutshell, Superfish not only injects ads into web pages, it intercepts encrypted traffic for every website you visit, Ars Technica explains. On secure HTTPS sites, Superfish assigns its own site certificate but makes you believe it's the actual site's official certificate. It gets worse, though: Attackers can use Superfish to launch man-in-the-middle attacks, intercepting your secure connections and stealing your passwords without you knowing.
If you have a Lenovo computer that shipped in 2014, you should definitely do this quick test below. (I have a Lenovo ThinkPad from that time, but got the all clear. I'm wondering if it's mostly lower end laptops that have been affected.) Whatever computer you're, using though, it doesn't hurt to check:
Visit Filippo Valsorda's Superfish test in either Chrome or Internet Explorer to see your results.
If you're infected, you might need to do a clean install of Windows to get rid of it, Forbes notes. Lifehacker also has instructions on removing the certificate--and then you'll have to retest to make sure Superfish is gone--but the safest thing is to do a clean install.