His goal was $5,000.
But the campaign had far exceeded that amount when it ended Friday night, raising more than $700,000.
A spokeswoman for the fundraising site Indiegogo said more than 30,000 people from all over the world contributed, with donations coming in from at least 84 countries and all 50 states. The site listed the raised amount as $703,873 Saturday morning.
Sidorov, a 25-year-old Canadian, came up with the idea for the monthlong campaign for the 68-year-old suburban Rochester grandmother. He said he was moved by a 10-minute video posted online showing Klein enduring profanity, insults and threats from middle school students on a school bus.
The school system in the town of Greece has suspended four seventh-grade students for a year. At least three of the boys issued written apologies to Klein.
Sidorov said he was as surprised as anyone with the final result of his posting, which also recorded nearly 28,000 comments.
"I think that people just love rallying around a great cause, especially helping someone in need or who has been abused or can't stand up for themselves," Sidorov said by phone from Toronto on Friday. "It just shows there are so many great people in the world. It warms my heart to see that."
He said he will soon launch a new drive with a goal of $7 million to combat bullying with counseling, a television series and a nonprofit social media website.
"Hopefully we can do a lot greater and bigger things stemming from what happened to Karen," he said.
"We keep in touch almost every day," he said. "We're good friends now."
Klein didn't immediately return telephone messages left at her home Friday.