In a major Hackers penetrated computer-optimization software CCleaner in a way that could have let them control millions of devices, Piriform, the company that makes the program, said Monday. A malicious program was planted inside the popular, free software, which is downloaded as often as 5 million times per week and is used to delete cookies and junk programs to make computers and Android phones run faster. Piriform said it estimates that 2.27 million people used the infected software, but downplayed any need for panic among consumers. “We resolved this quickly and believe no harm was done to any of our users,” the company said in a statement. Avast, the Czech Republic-based security software maker that bought Piriform in July, uncovered the attack on Tuesday. Two versions of the software released in August were affected, the company said.