What happened

Uber (UBER -2.50%). Western Digital (WDC -2.25%). SS&C Technologies (SSNC -3.40%).

What do the world's biggest ridesharing company, a maker of computer hard drives, and a software maker for the financial services and healthcare industries have in common? Not a whole lot -- except for one big thing: All three of these tech stocks are down more than 10% in Wednesday trading.

As of 12:40 p.m. EDT, Uber is down 19.2%, Western Digital 12.8%, and SS&C 14.2% -- and coronavirus is to blame.

3 red arrows going down and crashing through the floor

Image source: Getty Images.

So what

According to the World Health Organization, there are now more than 193,000 confirmed cases of COVID-19 worldwide. Deaths have surpassed 7,800, and 164 of the globe's 195 countries have reported cases of the disease -- that's 84% of all countries.

In Washington, there's talk of a $1 trillion bailout program -- and warnings from Treasury Secretary Steven Mnuchin that if it fails, we could see 20% unemployment in the U.S.  

Coronavirus may still require person-to-person contact to spread -- but there's panic in the air.

Now what

But that doesn't mean you should panic. Warren Buffett has famously said, when Wall Street is fearful, that's the best time for individual investors to get greedy, and buy stocks at a discount. I can tell you firsthand this is what I am doing right now.

For years, I've complained that stocks looked too expensive to buy, with the S&P 500 regularly topping eye-popping valuations of 25 times trailing earnings and more. Well, it doesn't cost that anymore. In fact, at an average P/E ratio of 17.8, the S&P to me looks like it's finally almost reasonably priced as a whole -- and within the index, there are certainly individual stocks to be found selling at even cheaper valuations.

When stocks as unrelated one to another as Uber, Western Digital, and SS&C all start plummeting in tandem, that's your cue that panic has set in -- and it may be your cue to buy.