Facebook is no longer classified as a tech stock.

There has probably never been a more fitting time to know exactly what’s in the ETFs and mutual funds your clients own. That’s because, as of today’s market open, some of the biggest names in technology including Facebook and Google will no longer be classified as such.

Major changes in the Global Industry Classification Standard (GICS), developed by MSCI and S&P Dow Jones Indices, have reclassified those stocks.

Facebook and Alphabet, the parent company of Google, move to the new communications sector, joining AT&T and Verizon.

The new sector combines networks and content from the telecommunications, information technology, and consumer discretionary sectors. It’s the second major change in GICS classification system in two years when real estate was removed from financial services to become its own sector.

(Related: Real Estate to Become Its Own S&P 500 Sector)

In the latest reclassification, Netflix, Comcast and Disney also move to the new communications sector, but from consumer discretionary, where Amazon will remain, joined by Alibaba Group and eBay from the technology sector.

“The changes are a step towards acknowledging the convergence of telecommunications, media, and select internet companies and the overlapping services rendered by these companies, within the GICS Structure,” S&P wrote in a note.  

(Related: Big Index Changes Are Coming Soon, and Many Advisors Are Unaware)

Comcast, for example, provides home and cell phone service through its Xfinity division, competing against AT&T and Verizon, but it is also a broadcasting company, which acquired NBC Universal, competing against AT&T, which owns Time Warner.

Verizon owns Yahoo, a competitor to  Google, which owns the Android operating system for cell phones.

“The lines are blurred as video and internet and phone service are offered by the same company,” says Todd Rosenbluth, senior director of ETF and mutual fund research at CFRA. The GICS sector changes are a  “good reminder not to not be passive about indexes,“ says Rosenbluth.

Sector ETFs are expected to be most affected by the GICS changes.

“If you own XLK in client portfolios understand it is different animal come Monday,” wrote Nicholas Colas, co-founder of DataTrek Research.  “The Technology Select Sector SPDR ETF will no longer hold Alphabet or Facebook.”

The two stocks together had a 15% weighting in XLK. In the new Communications Select Sector SPDR ETF (XLC), their combined weighting will top 40%. XLK will still hold Apple and Microsoft, but their combined weightings are expected to expected to increase as is Amazon’s in the Consumer Discretionary Select Sector ETF (XLY).

Other online retailers such as Alibaba Group and eBay move from the technology sector to consumer discretionary, joining Amazon.

Matthew Bartolini, head of SPDR Americas Research, recommends that advisors “know the changes” resulting from the new GICS classifications. “Know what tech will look like without Facebook in it. What that means for portfolios. Understand the impact of the changes. Know how to reposition.”

Complicating matters is the fact that not all ETFs are making these changes at the same time or at all. As of today, Vanguard and State Street have adjusted their funds to reflect the new GICS classifications. Vanguard had renamed its telecom ETF the Vanguard Communications Services Index Fund in June and the ETF, along with the Vanguard Consumer Discretionary and Technology ETFs began to track MSCI transitional indexes to reflect the new classifications. State Street launched its Communications Services Select Sector ETF (XLC) in June. 

But BlackRock, parent of iShares ETFs, notes on its website that iShares “do not follow GICS indexes, so are not directly affected by the changes.” The iShares Technology ETF (IYW) will  continue to hold Facebook and Alphabet along with Apple and Microsoft.

In addition to changes in many ETF holdings, the latest GICS classifications have other ramifications for advisors’ clients. They will, for example, affect the sector weightings in the S&P 500 as well as historical comparisons for sector funds.  

“If you use historical performance as a key factor in the decision-making to buy XLK, that data is close to worthless because Facebook and Alphabet, which have been driving portfolio, will no longer be in the portfolio,” says Rosenbluth. State Street has been working with clients to provide almost 20 years of adjusted historical returns so that they can make those comparisons, says Bartolini.