A giant logo is seen at Facebook's headquarters in London, Britain, December 4, 2017. REUTERS/Toby Melville

SAN FRANCISCO (Reuters) - S&P Dow Jones Indices and MSCI said on Thursday they would rename their Telecommunication Services Sector and add Comcast Corp, Netflix, Facebook and Alphabet to the newly broadened category.

In an overhaul of the Global Industry Classification Standard, or GICS, an industry taxonomy widely used by investors, the Telecommunication Services Sector will be expanded and renamed Communication Services, S&P Dow Jones Indices and MSCI said in a statement.

The new classification puts Facebook, Netflix and Google parent Alphabet - companies whose explosive growth has helped propel a stock-market rally - alongside traditional telecom players including AT&T Inc and Verizon Communications.

Indexes including the S&P 500 are a guide for trillions of dollars of capital worldwide, including index-tracking, exchange-traded funds (ETFs). Many of those funds track sector-specific indexes and could be affected by the GICS changes.

S&P Dow Jones Indices and MSCI said in November 2017 they were planning changes to the categories and that they would be implemented after the close of business on Sept. 28, 2018.

The updates are meant to reflect changes to industries resulting from technology and acquisitions.

Also moving to the newly named Communications Sector are Twitter Inc and Snap Inc, both currently part of the Information Technology Sector.

Walt Disney Co and DISH Network Corp, both currently in the Consumer Discretionary Sector, will also join the Communications Sector.

Comcast and Netflix currently fall under the Consumer Discretionary Sector, while Alphabet and Facebook are currently in the Information Technology Sector.