Anonymous hackers have reportedly accessed U.S. government computers in multiple agencies and stolen information, the FBI warned this week. The hackers took advantage of a a flaw in Adobe's ColdFusion software to break into computers in a campaign that started a year ago, Reuters reported on Friday citing an FBI memo the news agency obtained. Hackers left "back doors" to return to many of the machines as recently as last month, Reuters added.

The memo described the attacks to the U.S. Army, Department of Energy, Department of Health and Human Services, and perhaps many more agencies.

The FBI document tells system administrators what to look for to determine if their systems are compromised.

Neither the FBI nor Adobe Systems have officially commented on the report.