BEIJING — Jing Yuechen, the founder of an Internet start-up here in the Chinese capital, has no interest in overthrowing the Communist Party. But these days she finds herself cursing the nation’s smothering cyberpolice as she tries — and fails — to browse photo-sharing websites like Flickr and struggles to stay in touch with the Facebook friends she has made during trips to France, India and Singapore.

Gmail has become almost impossible to use here, and in recent weeks the authorities have gummed up Astrill, the software Ms. Jing and countless others depended on to circumvent the Internet restrictions that Western security analysts refer to as the Great Firewall.

By interfering with Astrill and several other popular virtual private networks, or V.P.N.s, the government has complicated the lives of Chinese astronomers seeking the latest scientific data from abroad, graphic designers shopping for clip art on Shutterstock and students submitting online applications to American universities.

“If it was legal to protest and throw rotten eggs on the street, I’d definitely be up for that,” Ms. Jing, 25, said.