It appears that Soviet intelligence had many victories during the Cold War, infiltrating the UK and the United States with relative ease and getting access to critical information. At the same time, Western Intelligence had seemingly little success in doing the same. Why? Is this just a myth?
Have you read Billion Dollar Spy? The US gleaned insane amounts of data about Russian weapons capabilities from a single source.
Also, the US intelligence community operated a little differently than the Soviets as it was easier to be a Russian in the US than an American in Russia.