Symantec finds 5 out of the 6 most commonly used words in spam have exclamation points. These punctuation marks activate the human alarm system -- speeding up brain processes and exaggerating judgment calls, according a social psychology professor at Utrecht.

Five out of the six most commonly used words in spam include exclamation points, according to Symantec Corp. The top six words, based on a snapshot of spam sent globally during one week in March, include: shipping!, today!, here!, fingertips! online! and available.

Mathew Nisbet, malware data analyst at Symantec Hosted Services, posted his analysis of word usage in spam on a Symantec blog. "Spammers like to create a sense of urgency in their messages, as the less time someone spends thinking about it, the less likely they are to realize it is in fact a scam of some type," he writes.

Symantec doesn't have statistics on how many people actually fall for this tactic -- or whether the technique even works.

But the sight of an exclamation mark does have a powerful affect on people, according to Kees van den Bos, a professor in the Department of Social and Organizational Psychology at Utrecht University in the Netherlands.

"People are affected strongly by these kinds of punctuation marks," said Van den Bos, who conducted studies on the impact exclamation marks and flashing lights have on the justice judgment process.

His research, published online by the Journal of Experimental Social Psychology in 2008, found that exposure to exclamation points reduces response times and exaggerates judgments. People took less time to determine whether a situation was fair or unfair and their justice judgment calls were more extreme.

For example, a situation perceived as unfair would be "very" unfair. "People really become more vigilant ... reacting faster and more strongly towards things that are fair or unfair," said Van den Bos.

In another study, Van den Bos used an fMRI (functional magnetic resonance imaging) scanner to assess the brain processes of participants watching exclamation marks compared to other controlled stimuli.

Exclamation points activated the medial prefrontal cortex -- an area of the brain that becomes activated when people are processing information that is very emotional and perhaps alarming, he said. "You are really processing much faster than when you didn't see an exclamation mark," he said.

When you are exposed to an exclamation mark, your whole system becomes activated, which starts the process of trying to make sense of the situation and determine whether or not you should pay attention, said Van den Bos.

This isn't the same as panicking, he added. It's the process before this -- when you try to interpret the situation and analyze what to do next, he said. "People try to make sense of whether they should fight or flight ... but aren't sure yet," he said.

Other studies involving question marks produced quite different results, said Van den Bos. "You don't get this activation of the alarm system ... it really seems to be the exclamation mark that is doing the trick," he said.