(CNN) -- AC/DC rhythm guitarist Malcolm Young is ill and is "taking a break," the band posted on its website Wednesday.
But the hugely popular group will continue, AC/DC said in the statement.
"After forty years of life dedicated to AC/DC, guitarist and founding member Malcolm Young is taking a break from the band due to ill health. Malcolm would like to thank the group's diehard legions of fans worldwide for their never-ending love and support," the statement said.
"In light of this news, AC/DC asks that Malcolm and his family's privacy be respected during this time. The band will continue to make music."
Young, 61, formed the group in 1973 in Sydney, Australia, with his brother Angus. The statement did not reveal what his illness was, though rumors have swirled since an e-mail was sent to a Perth, Australia, radio station earlier this week.
Mark Gable, a fellow musician, told Australia's ABC Radio that Malcolm Young "is sick. ... It's not just that he is unwell, it's that it is quite serious." Gable's remarks were reported in the Sydney Morning Herald.
The hard-rocking group, whose albums include the multimillion-selling "Back in Black" and "For Those About to Rock (We Salute You)," quickly rose in the music world thanks to their terse riffs and tireless touring. Lead guitarist Angus Young, then and now, is known for wearing a schoolboy uniform on stage.
Bon Scott, who sang lead for the band in the '70s, died in 1980 just as "Highway to Hell" became AC/DC's breakthrough album. He was replaced by Brian Johnson, who sang on AC/DC's biggest chart hits, including "You Shook Me All Night Long" and "Thunderstruck."
The group has continued putting out million-sellers to the present day. AC/DC's most recent studio album, "Black Ice" (2008), debuted at No. 1 in 29 countries -- including the United States -- sold 6 million copies and produced the Grammy-winning track "War Machine." It was the second biggest-selling album of the year.
Malcolm Young's guitar has been a major part of the AC/DC sound -- a sound often slammed by rock critics but beloved by fans of hard rock and heavy metal. Other guitarists, including Megadeth's Dave Mustaine, rank him highly.
Young has said he's proud of the band's straightforward, powerhouse crunch.
"People can go out and hear R.E.M. if they want deep lyrics, but at the end of the night, they want to go home and get f*****! That's where AC/DC comes into it," he once said.
AC/DC is one of the biggest-selling bands in music history, ranking 10th on the Recording Industry of America list with more than 70 million albums sold.