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Since the early post-9/11 years, Americans have expected terrorism.

Majorities have said they think "occasional acts of terrorism in the U.S. will be a part of life in the future," when the Pew Research Center has asked-74 percent thought so in 2003-and while expectations of terrorism have dipped in recent years, the Boston marathon attacks rejuvenated them.

After polling in the low-to-mid-60s since 2009, expectations of future terrorism jumped from 64 percent last April to 75 percent today. Pew began its most recent survey of 1,002 adults on Thursday, three days after Tamerlan and Dzokhar Tsarnaev allegedly detonated two bombs in downtown Boston, killing three people and injuring scores of bystanders.

A week later, the Boston attacks have most dramatically influenced younger Americans.

The increase spans demographics, but the groups that expected terrorism the least in 2012 - 18-to-29-year-olds (54 percent), 30-to-49-year-olds (62 percent), and Democrats (60 percent) - have been brought in line with older respondents and Republicans. Now, at least 74 percent say they expect future attacks, across all those groups. The gap between 18-to-29-year olds and those 65 and older, 20 percentage points last year, is now only 5 after the youngest demographic grew to expect future terrorism by 20 percentage points.

At the same time, Americans' aren't any more "worried" about another imminent attack.

When Pew asked how "worried" its respondents were that "there will soon be another terrorist attack in the United States," 23 percent said they were "very" worried, while 35 percent said they were "somewhat" worried. While the numbers have ebbed and flowed in previous years, today's results fall well within the norm. In 2006, results matched the post-Boston 23-percent who were "very" worried. In 2005, it was 26 percent. Today, 41 percent say they're "not too" worried or not worried at all-more than have said so since August 2003.

In other words: After Boston, more Americans think occasional attacks will be a part of life in the U.S., but no more are "worried" about a new attack happening soon, and in fact more say they're not worried about it than at any point in the last nine years.