Weird. I got the same thing in one of my clients index.html with a bunch of other mysterious files. Perhaps they got into his FTP. of my 50 other clients, noone else was effected it seems.
Upon inspection random users have been been able to access the FTP for a while. here was the unique list of IPs that I know aren't the owner's
137.149.150.100
173.35.246.173
174.143.242.47
188.229.31.45
188.24.43.62
188.25.239.153
188.25.73.186
189.28.154.133
198.145.116.71
198.63.210.170
203.81.55.153
208.101.102.60
209.239.120.50
212.189.180.1
213.142.137.131
217.27.224.7
68.45.8.194
69.143.233.198
70.38.11.176
70.81.249.108
74.58.67.48
76.104.123.11
78.159.45.198
78.245.136.34
78.251.215.23
78.94.44.177
79.112.216.109
79.114.26.35
79.117.237.130
79.136.32.209
81.66.237.244
81.82.154.174
81.82.52.12
82.234.154.97
82.247.130.26
82.36.17.105
83.84.225.144
84.196.204.172
85.136.145.183
85.139.199.26
85.28.76.190
86.60.215.133
87.244.217.188
87.247.251.44
87.59.67.145
88.162.127.32
88.207.7.151
89.114.92.59
89.46.96.87
89.47.179.66
91.147.207.215
91.65.157.38
92.249.196.99
94.141.145.147
94.227.112.143
95.79.22.165
99.226.133.161
Looks like some sort of mass attack. I would look at the timestamp on the files that were modified, see if any are close or if any of your other ftp people have logged in with those IPs. Just to note I am running debian linux server with proftpd...
I got a weird error message when trying to edit the file in winSCP using notepad2...so it looks like whatever code it is, messing up typical text editors. I was able to nano the file and delete the links though.
PS: I was made aware of this when google emailed me "Dear site owner or webmaster of [censored].com,
We recently discovered that some of your pages can cause users to be infected with malicious software. We have begun showing a warning page to users who visit these pages by clicking a search result on Google.com."