is this a false positive?

Viruses and worms
1

avast detected that chromerecovery.exe and googleupdate inside the avast sandbox are infected by rootkits

is it acting up or so I have something to worry about?

2

not easy to say just from a file name…

upload suspicious file(s) to www.virustotal.com and test with 40+ malware scanners

alternatives: www.metascan-online.com www.jotti.org

3

its located in C:\avast! sandbox and I cannot find a way to get into this folder.

4

Hi CosmicRave

Probably a FP: https://www.virustotal.com/nl/file/9b0acf240bf715cb6d1f2db5a73ec8a2b2e08c303c612a32bd98cd7ce6db3dec/analysis/
Norton also came up with this FP earlier: http://productforums.google.com/forum/#!topic/chrome/srpgqCsMBRY
If indeed malcoded, s the detection for files with the name “sfc.dll” that replace the original “sfc.dll” file. The original “sfc.dll” may have been placed by malware into another location within the same computer. So an infected sfc.dll should be in another location on that infested computer.
If in doubt you could ask the qualified removal experts to check this for you. As you report it for inside avast! sandbox it could be an incompatibility issue…
then report from inside your av solution directly to avast!

polonus